Giant chlorine isotope effect of ion-molecule reaction

Giant chlorine isotope effect of ion-molecule reaction | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Giant chlorine isotope effect of ion-molecule reaction Shan Tian, Yaya Zhi, Jie Hu, Jingchen Xie, Chun-Xiao Wu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5605490/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Isotope substitution profoundly influences chemical reactions, signifying different reaction rates due to mass-related nuclear quantum effects. Due to the smaller mass-difference ratio, heavy-atom isotope effect is usually much weaker than the hydrogen/deuterium effect, which has been the underlying principle for chemical isotope labelling, a prevailing technique of environmental assessments. Here we report a giant chlorine ( 35,37 Cl) isotope effect of the collisional reactions between iso -dichloroethylene (naturally comprising 35,37 Cl-isotopologues) and argon ion. As a grave challenge to conventional understandings, we find that the isotopic signature δ 37 Cl of the dehydrochlorination channel is one thousand times larger than the regular values, namely, an extraordinary priority of the product C 2 H 37 Cl + . Hydrogen-atom scrambling and roaming assisted 35 Cl-elimination mechanisms are proposed for this unprecedentedly strong isotope effect. Our finding adds a new dimension of isotope effects and enlightens related methodological renovations of environmental assessment. Physical sciences/Chemistry/Physical chemistry/Reaction kinetics and dynamics Earth and environmental sciences/Environmental sciences/Environmental chemistry/Environmental monitoring Figures Figure 1 Figure 2 Figure 3 Figure 4 Full Text Isotopes carry the messages of molecular creations and transformations. Accordingly, chemical isotope labelling has been a powerful tool for multidisciplinary applications, such as characterizing chemical mechanisms, dating climate change and life origin on the Earth and tracing environmental pollutants 1-7 . Different kinetic effects are exhibited in isotope fractionations and are generally classified into mass-dependent and mass-independent ones 4-6 . The mass-independent effect, mostly ascribed to nuclear spin and magnetic moment, was observed in the chemical reactions under magnetic field 6 . On the contrary, the mass-dependent effect, as a classic content in textbooks, arises from zero-point vibration and quantum tunneling 4-7 , in which hydrogen/deuterium (H/D) isotopologues show the most prominent effect 4 . Heavy-atom isotopic effects, except from the nuclear spin, are usually very weaker or negligible because of the smaller isotopic mass difference ratio (Δ m/m ). Here we report the extraordinary anomalies of chlorine ( 35,37 Cl) isotope effect in the dechlorination and dehydrochlorination of iso -dichloroethylene (H 2 C=CCl 2 ) by collisions with argon ion (Ar + ). The isotope signatures δ 37 Cl of the backward-scattered C 2 H 2 Cl + (via the dechlorination) and C 2 HCl + (via the dehydrochlorination) yields reach extremely large values, namely, three to four orders higher than the regular δ 37 Cl values. Since 35,37 Cl isotopes have the same nuclear spin and the present dechlorination and dehydrochlorination proceed in a field-free region, this giant isotope effect is irrelevant to the nuclear spins or magnetic moments, thus certainly beyond current models of the heavy-atom isotope effect. Polychlorinated hydrocarbons are widespread toxicants and groundwater contaminants, and the δ 37 Cl value is a key index of atmospheric and environmental assessments 2,7-9 . However, the Cl-isotope effects of polychlorinated hydrocarbons are diverse and understood insufficiently, primarily due to multiple Cl-isotope fractionation pathways of coexisting isotopologues 7-10 . Three isotopologues of iso -dichloroethylene, C 2 H 2 35 Cl 2 (57.4%), C 2 H 2 35 Cl 37 Cl (36.7%) and C 2 H 2 37 Cl 2 (5.9%), coexist as the reagents in the present experiments, where their concentrations are determined with the natural abundance ratio 1 : 3.125 of 37 Cl : 35 Cl (ref. 10). The isotope ratio of the products can be measured with high-precision mass spectrometry, ever since the pioneering work by Nier and collaborators 11 . For the C-Cl bond cleavage of the monochlorinated compound, the chlorine kinetic isotope effect (KIE) is expressed with the KIE Cl value equal to k 35 / k 37 , where k is the Cl-elimination rate constant. The Streitwieser semiclassical limit of KIE Cl is 1.013 (ref. 12), considering the frequency difference between C- 35 Cl and C- 37 Cl bond stretching (a typical mass-dependent effect). For the dechlorination or dehydrochlorination of a dichlorinated compound, the δ 37 Cl value is determined by, $$\:{\delta\:}{}^{37}Cl=\left(\frac{{}^{37}{Cl}_{p}/{}^{35}{Cl}_{p}}{{}^{37}{R}_{std}}-1\right)\bullet\:1000$$ 1 $$\:\frac{{}^{37}{Cl}_{p}}{{}^{35}{Cl}_{p}}=\frac{a{\bullet\:KIE}_{Cl}+b}{c{\bullet\:KIE}_{Cl}+d}$$ 2 where R std is the isotope ratio of the standard free ion ( 37 R std of C 2 H 2 Cl + equals 0.32), Cl p corresponds to the ion intensity of Cl-isotopic products measured with the mass spectra and the parameters a = 0.426, b = 0.059, c = 0.574, and d = 0.941 (Table S1 and section 1 of Supplementary Information). The 37 Cl-yields are bound to the minor reagents C 2 H 2 35 Cl 37 Cl and C 2 H 2 37 Cl 2 , thus the upper limit of δ 37 Cl is about 1319‰ by assuming that all C 2 H 2 35 Cl 37 Cl reagents undergo the 35 Cl-elimination after the charge transfer. In the present work, we find that δ 37 Cl values are significantly larger than the value of the mass-dependent effect (δ 37 Cl ≈ 7‰ for the Streitwieser limit) and the upper limit. Mass spectrometry, as a straightforward method to determine the isotope ratio, is frequently frustrated in exploring the dynamics mechanism, thus more powerful experimental techniques are demanded for these extremely large δ 37 Cl values. Recently, many efforts have been put into investigating the H/D isotope effect with state-of-the-art techniques 13 – 15 , emphasizing the unexpected slowness of reactions, the intermediate complex, or the scrambling dynamics. Scrambling or roaming is a fascinating mechanism 16 , in which two fragments of molecular decomposition have insufficient translational energies to separate and their roaming around each other is followed with an exothermic internal abstraction. An indirect roundabout mechanism was also found in the nucleophilic substitution reaction between Cl¯ and CH 3 I (ref. 17). The scrambling or roaming mechanism opens a door to unusual reactions and possibly leads to peculiar isotope effects. To the best of our knowledge, such a fundamental issue has never been touched. Using three-dimensional ion velocity map imaging (3D-VMI) 18 , 19 measurements and with the help of ab initio molecular dynamics (AIMD) simulations, we unveil an extremely strong isotope effect (δ 37 Cl ≈ 10 5 ‰) for the backward-scattered C 2 HCl + yield of dissociative charge exchange (DCE) reaction Ar + + iso -C 2 H 2 Cl 2 → Ar + HCl + C 2 HCl + , and suggest that this remarkable effect is attributed to the H-scrambling and roaming dynamics. The 3D-VMI measurements were carried out with our crossed-beam apparatus 19 . As shown in Fig. 1a, the apparatus consists of a well-confined pulsed Ar + ion beam 20 , a supersonic molecular beam, an ion VMI optics system, and a delay-line ion detector to realize the 3D imaging. The 3D-VMI technique enables us to simultaneously record the velocity distributions and the time-of-flight (TOF) mass spectra of different ionic yields. The VMI technique is based on the TOF mass spectrometry, but two ions with a small mass difference are generally undistinguishable in the VMI measurement because of the flight-time overlapping of two adjacent ionic Newton spheres 18 . Fortunately, as shown in Fig. 1b, the Cl-isotopologues of the parent ion C 2 H 2 Cl 2 + (the charge-exchange-only yield) and the DCE yields (C 2 HCl 2 + , C 2 H 2 Cl + , and C 2 HCl + ) are disentangled, partially owing to a proper TOF length (ca. 46.1 cm) of our VMI apparatus 19 . At four collision energies in the center-of-mass (c.m.) reaction coordinate (E c.m .) 2.58, 3.95, 4.67, and 8.90 eV for C 2 H 2 35 Cl 2 (E c.m . values are slightly different for the minor reagent C 2 H 2 35 Cl 37 Cl or C 2 H 2 37 Cl 2 ), the productions of the parent ion C 2 H 2 Cl 2 + and the dehydronated yield (C 2 HCl 2 + ) are much lower than those of C 2 H 2 Cl + and C 2 HCl + . According to the fitted profiles in the TOF spectra (Fig. 1b), we obtain the individual contributions of the Cl-isotopic ions, where each contribution corresponds to the whole Newton sphere of a certain type of these ions. Then, a velocity image can be obtained by slicing the Newton sphere at the equator with a time thickness of 60 ns in the off-line data analyses 19 , 21 – 24 . Owing to the low velocities of ionic yields and the large apertures of the VMI electrodes, the ion collection efficiency reaches nearly a hundred percent. As shown in Table S2, we obtain the branching ratios of different channels and the production ratios. With reference to the 37 R std values 0.32 of the free ions C 2 H 2 Cl + and C 2 HCl + , we further obtain the δ 37 Cl values using Eq. (1) and plot their collision-energy dependences in Fig. 1c. Generally, the δ 37 Cl values of C 2 H 2 Cl + and C 2 HCl 2 + slightly fluctuate around the Streitwieser limit, indicating a normal weak Cl-isotope effect. To our surprise, the extremely large δ 37 Cl values, about 10 4 ‰, are observed for C 2 HCl + . According to Eq. (2), these δ 37 Cl values correspond to 3.33 of the ratio C 2 H 37 Cl + / C 2 H 35 Cl + (also see Table S2) which is out of the regular range, namely, from 0.063 as KIE Cl < > 1. A question instantly arises: what dynamic process leads to such extraordinary anomalies? Figure 2 shows the sliced velocity images of the C 2 H 2 Cl + and C 2 HCl + isotopic yields, while the C 2 HCl 2 + images are exhibited in Fig. S1 and not discussed due to the much lower production efficiency. To our surprise again, in Fig. 2 we observe the remarkable collision-energy dependences and the significant distribution differences between the 35 Cl- and 37 Cl-species, implying that the reaction dynamics underneath these images should be more complicated than what we surmised from Fig. 1c. Even for the seemingly normal isotope effect of C 2 H 2 Cl + (see the middle panel of Fig. 1c), the image differences between C 2 H 2 35 Cl + and C 2 H 2 37 Cl + also indicate a remarkable dynamic isotope effect. At a given collision energy, for instance, E c.m . = 2.58 eV, most 35 Cl-species of the C 2 H 2 Cl + or C 2 HCl + yields are confined in the forward (along the flying direction of the reagent molecule) region and along the collision axis, while a bimodal distribution is observed clearly for the 37 Cl-species. In the latter, the backward (along the flying direction of the reagent Ar + ) distribution is highlighted with a green frame, as shown in Figs. 2a and 2e. Furthermore, the backward distribution of C 2 H 2 37 Cl + or C 2 H 37 Cl + observed at the lower collision energy (Figs. 2a, 2e) fades down (Fig. 2d) or changes to be a little forward (Fig. 2h) at the higher collision energy. To have insights into the dynamic isotope effect, in Fig. 3 we plot the velocity dependences of δ 37 Cl for C 2 H 2 Cl + and C 2 HCl + yields at the lowest collision energy. Note that the weighing factors at different velocities are not considered. The δ 37 Cl values of the much slower C 2 H 2 Cl + ( u x ~ 0 m/s) are close to zero and absent in Fig. 3a, due to the unusual 37 Cl-elimination through a long-lived intermediate. In contrast, a high preference of 35 Cl-elimination leads to the large δ 37 Cl values. As shown in Fig. 3a, the backward C 2 H 2 Cl + ions with velocities larger than 1000 m/s are located out of the yellow-colored region. As mentioned above, this yellow-colored region covers a δ 37 Cl range with the assumed upper limit 1319‰. Most δ 37 Cl values of C 2 HCl + , as observed in Fig. 3b, evidently overtop this yellow-colored range, and exhibit a maximum of 10 5 ‰ for the backward-scattered ions with the velocity about 600 m/s. In the following discussion, we focus on the extraordinary preference of 35 Cl-elimination. To elucidate the observations, we need to recall basic features about the DCE dynamics of the collisions with Ar + (refs. 19–24): (i) In the large impact-parameter or peripheral collision, the parent and large daughter ionic yields are scattered forward with the velocities close to that of the reagent molecule, and the co-product Ar atom serves as a spectator. (ii) A small impact-parameter or intimate collision facilitates an efficient translational-to-internal energy transformation, then the backward-scattered ions can be produced from the rebounded intermediate. (iii) Due to the long-distance attraction, a randomly oriented molecule can be spatially aligned or oriented during the ion approaching. In the present case, the daughter ions C 2 H 2 Cl + and C 2 HCl + show more delocalized distributions (Fig. 2), while the heavier ion C 2 HCl 2 + is located around the molecular reagent position (as shown in Fig. S1 ). The forward C 2 H 2 Cl + and C 2 HCl + could be produced quickly in the large impact-parameter DCE reaction; On the contrary, the backward C 2 H 2 Cl + and C 2 HCl + should be attributed to the relatively slow dissociations of the rebounded iso -C 2 H 2 Cl 2 + formed by the small impact-parameter or head-on collision. In the latter, the iso -C 2 H 2 Cl 2 + structure could be deformed seriously and subsequently dissociate, where the isotopic competition is responsible for the Cl-isotope effect of the backward C 2 H 2 Cl + and C 2 HCl + . We perform the AIMD simulations (Supplementary Information, Figs. S2, S3) to mimic the head-on collisions at the lowest collision energy. Firstly, a comparison between the C- 35 Cl and C- 37 Cl bond ruptures in two representative trajectories is described in Fig. 4a. The C- 37 Cl bond cleavage lags much behind the C- 35 Cl bond, leading to the 35 Cl-elimination preference; then C 2 H 2 37 Cl + survives via the more active C- 37 Cl stretching motion. This is in line with the normal mass-dependent isotope effect: the C- 37 Cl bond energy is a little higher than the C- 35 Cl bond, due to the lower zero-point vibrational energy of the former; the vibrational-state density of the C- 37 Cl stretching is higher than that of the C- 35 Cl stretching, because of the smaller vibrational-state energy interval of the C- 37 Cl stretching. Two representative trajectories of the dehydrochlorination are plotted in Fig. 4b. One can find the H atom scrambling or roaming before the 35 Cl-abstraction. It is noted that, in the dissociative photoionization, Cl-atom scrambling in the vicinity of the two-pathway crossing was proposed by scanning the C-Cl and C-H bond lengths on the potential energy surface 25 . In the present on-the-fly AIMD results, the dynamic processes (Fig. S3) are roughly classified into the fast (case a ) and slow (case b ) types. In case a (also see movie S1), the H atom at the 35 Cl side scrambles quickly before the 35 Cl-abstraction. In case b (also see movie S2), the H atom at the 37 Cl side roams from -C β H 2 to -C α Cl 2 , an intermediate Cl 2 C α H-C β H + is formed temporarily, and then this H atom transfers back to the C β end and goes to the 35 Cl side via a roundabout route, finally abstracting the 35 Cl atom. The dynamic processes to produce C 2 H 2 Cl + and C 2 HCl + could start from \(\:\stackrel{\sim}{\text{F}}\) state (the sixth valence-exited state) of iso -C 2 H 2 Cl 2 + (ref. 26) after the prompt charge transfer from Ar + to iso -C 2 H 2 Cl, but those AIMD computations are unaffordable due to state-to-state nonadiabatic propagations within multiple degrees of nuclear motion freedom. Some limitations of the present simulations are also addressed in section 3 of Supplementary Information. Nevertheless, the 35 Cl-elimination assisted with the H-atom scrambling or roaming is a heuristic model, in which the Cl-isotope effect can be magnified with more than one thousand times. Our finding paves a way to a piece of virgin land of heavy-atom isotope effects. Moreover, this work potentially advances the isotope fractionation techniques and provokes to refine the heavy-atom isotope labelling protocols. Declarations Data availability The data that support the findings of this study are included in the paper, and Supplementary Information and Supplementary Videos are available online or from the corresponding author upon the request. Acknowledgements We thank supported by National Natural Science Foundation of China (22233004) and the Innovation Program for Quantum Science and Technology (2021ZD0303303). The numerical calculations were done in the Supercomputing Center of USTC. We appreciate Prof. Jun Jiang’s help on the computational source and the valuable discussions with Prof. Yi Luo. Author contributions YZ and JH carried out the experiments. YZ did the theoretical simulations. JCX and CXW participated in the calculations and experimental operations, respectively. YZ, JH and SXT performed the data analyses. YZ, JH and SXT contributed to drafting the manuscript. JH and SXT conceived the project, SXT supervised this work. Competing interests The authors have no competing interests to declare. Additional information Supplementary information The experimental and AIMD simulation methods and additional results, supplementary videos) available at… Correspondence and requests for materials should be addressed to S.X.T. References Griffiths H (1998) Stable isotopes. Integration of Biological, Ecological and Geochemical Processes. Bios Scientific Laube JC, Kaiser J, Sturges WT, Bönisch H, Engel A (2010) Chlorine isotope fractionation in the stratosphere. 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Chin J Chem Phys 36:509–516 Bodi A, Stevens WR, Baer T (2011) Understanding the complex dissociation dynamics of energy selected dichloroethylene ions: Neutral isomerization energies and heats of formation by imaging photoelectron-photoion coincidence. J Phys Chem A 115:726–734 Locht R, Dehareng D, Leyh B (2017) The photoelectron spectroscopy of the dichloroethylenes: the geminal isomer 1,1-Cl 2 C 2 H 2 . An experimental and quantum chemical study. J Phys Commun 1:055030 Additional Declarations There is NO Competing Interest. Supplementary Files movieS1.mp4 movie s1 movieS2.mp4 movie s2 msSI.pdf Supplementary Information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5605490","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":391896825,"identity":"fe5e3163-326d-4a4a-a7ab-6ace2b7e6ba3","order_by":0,"name":"Shan Tian","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYJCCAwwMNlAmG1EamEFa0qCqidUCBIdJ0CI/I//ggZ87zifOn9/8gOFD2WEG/tkN+LUYnDnMcLD3zO3EDcfYDBhnnDvMIHHnAAEt7M0MB3jbgFrYeBiYedsOMxhIJBBwWDMzw8G/becS57cBtfwlRgvD8WaGw7xtBxIbjgG1MBKjBegXg8OybcnGG46lGRzsOZfOI3GDkMNmJD7++LbNTnZ+8+GHD36UWcvxzyDkMGRwAIh5SFA/CkbBKBgFowAXAABbMURCpJosBwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-2836-6277","institution":"University of Science and Technology of China","correspondingAuthor":true,"prefix":"","firstName":"Shan","middleName":"","lastName":"Tian","suffix":""},{"id":391896826,"identity":"57955d46-8dde-4025-987e-66783776a130","order_by":1,"name":"Yaya Zhi","email":"","orcid":"","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Yaya","middleName":"","lastName":"Zhi","suffix":""},{"id":391896827,"identity":"2f36e03b-c887-4d89-b568-d27db4093ffd","order_by":2,"name":"Jie Hu","email":"","orcid":"https://orcid.org/0000-0002-6956-4651","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Jie","middleName":"","lastName":"Hu","suffix":""},{"id":391896828,"identity":"3b0abaa7-afe1-4230-9e5e-cf5c798a81bc","order_by":3,"name":"Jingchen Xie","email":"","orcid":"https://orcid.org/0009-0007-8623-1916","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Jingchen","middleName":"","lastName":"Xie","suffix":""},{"id":391896829,"identity":"c3adf322-b842-4937-bc46-b4ebebb74a8e","order_by":4,"name":"Chun-Xiao Wu","email":"","orcid":"","institution":"University of Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Chun-Xiao","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2024-12-09 03:40:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5605490/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5605490/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71833329,"identity":"9fd03104-d946-4133-9c3b-8b516c2dcd56","added_by":"auto","created_at":"2024-12-19 03:27:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":255422,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic of the crossed-beam velocity map imaging apparatus and some mass-spectral results of ion-molecule reactions between Ar\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e and \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eiso\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-dichloroethylene. a\u003c/strong\u003e, Newton sphere (colored in orange) of the ionic yields is formed and expanded in the ion optics system.\u003cstrong\u003e b\u003c/strong\u003e, The time-of-flight mass spectra recorded at 4.67 eV for the reagent C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e or 4.70 eV for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl are selectively presented. The C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) and C\u003csub\u003e2\u003c/sub\u003eH\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e ions are not observed due to the much lower concentration of \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e in the molecular beam. \u003cstrong\u003ec\u003c/strong\u003e, The C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e ionic yields show near-zero values of the isotope signature δ\u003csup\u003e37\u003c/sup\u003eCl (dashed black line), while the δ\u003csup\u003e37\u003c/sup\u003eCl values of the C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e yield (dashed pink line) are very high.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/3bab9d1ab2a62ddab1c7147d.png"},{"id":71833328,"identity":"1605f772-2066-4973-92ac-51101c2fd7d4","added_by":"auto","created_at":"2024-12-19 03:27:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":206936,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTime-sliced velocity images of the isotopic products C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eCl\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e and C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eHCl\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e. \u003c/strong\u003eIn the left panels, the collision energies in the center-of-mass (c.m.) coordinate for the reagent C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e are 2.58 (\u003cstrong\u003ea\u003c/strong\u003e, \u003cstrong\u003ee\u003c/strong\u003e), 3.95 (\u003cstrong\u003eb\u003c/strong\u003e, \u003cstrong\u003ef\u003c/strong\u003e), 4.67 (\u003cstrong\u003ec\u003c/strong\u003e, \u003cstrong\u003eg\u003c/strong\u003e) and 8.90 (\u003cstrong\u003ed\u003c/strong\u003e, \u003cstrong\u003eh\u003c/strong\u003e) eV. In the right panels, they are 2.60 (\u003cstrong\u003ea\u003c/strong\u003e, \u003cstrong\u003ee\u003c/strong\u003e), 3.98 (\u003cstrong\u003eb\u003c/strong\u003e, \u003cstrong\u003ef\u003c/strong\u003e), 4.70 (\u003cstrong\u003ec\u003c/strong\u003e, \u003cstrong\u003eg\u003c/strong\u003e) and 8.95 (\u003cstrong\u003ed\u003c/strong\u003e, \u003cstrong\u003eh\u003c/strong\u003e) eV for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl. The ion intensities in each image are normalized independently. The velocities in the laboratory (\u003cem\u003ev\u003c/em\u003e\u003csub\u003eAr+\u003c/sub\u003e, \u003cem\u003ev\u003c/em\u003e\u003csub\u003eM\u003c/sub\u003e) and center-of-mass (\u003cem\u003eu\u003c/em\u003e\u003csub\u003eAr+\u003c/sub\u003e, \u003cem\u003eu\u003c/em\u003e\u003csub\u003eM\u003c/sub\u003e) coordinates are shown with broken and solid white lines, respectively. The forward (left) and backward (right) scattering directions are defined with respect to the center of mass (red circle). In the right panels of (\u003cstrong\u003eA\u003c/strong\u003e) and (\u003cstrong\u003eE\u003c/strong\u003e), the backward distributions are framed in green color for eye-catching.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/9927ca1d4e64aa02726bc953.png"},{"id":71833326,"identity":"69aafa64-f7b6-4bb0-af8f-65d2eae491aa","added_by":"auto","created_at":"2024-12-19 03:27:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":162658,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVelocity dependences of the δ\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e37\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003eCl values\u003c/strong\u003e \u003cstrong\u003efor C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eCl\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e (a) and C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eHCl\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e (b) yields produced at the lowest collision energy. \u003c/strong\u003eSome experimental data are missed due to their values close to zero. The negative and positive velocities represent the forward- and backward-scattered ions, respectively. A range of δ\u003csup\u003e37\u003c/sup\u003eCl with an upper limit 1319 ‰ estimated with eqs. (1) and (2) is shown in yellow. The experimental δ\u003csup\u003e37\u003c/sup\u003eCl values that are out of the yellow region should be attributed to specific mechanisms beyond current models.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/36e85f7d909fc92e3866b7a3.png"},{"id":71833332,"identity":"f8bce396-50d8-4f86-8068-b0e9cfa124be","added_by":"auto","created_at":"2024-12-19 03:27:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":338557,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAIMD simulation results of the head-on collision reactions of Ar\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e+\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e with \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eiso\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e-C\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003csup\u003e\u003cstrong\u003e35\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003eCl\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e37\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003eCl. a\u003c/strong\u003e, Isotopic differences are exhibited with Cl-eliminations (upper) and C-Cl stretching motions (bottom) in the dechlorination processes. The arrows in the upper panel indicate the different times of the C-Cl bond cleavage. \u003cstrong\u003eb\u003c/strong\u003e, Representative snapshots of the dehydrochlorination processes (case \u003cem\u003ea\u003c/em\u003e, from 0 to 117 fs; case \u003cem\u003eb\u003c/em\u003e, from 183 to 316 fs) are depicted, in which the H-atom scrambling (case \u003cem\u003ea\u003c/em\u003e) and roaming (case \u003cem\u003eb\u003c/em\u003e) are highlighted with the yellow curves and Ar atoms are rebounded.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/da234914a167e8d4a1e56534.png"},{"id":75331636,"identity":"d7244191-3a7c-48fe-8968-49f138eeb2fe","added_by":"auto","created_at":"2025-02-03 12:29:20","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1733100,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/1be1dcac-9312-4790-a92f-5e6c7ea7eaf9.pdf"},{"id":71833331,"identity":"4f264544-5c2c-491e-89fe-2da1213c2454","added_by":"auto","created_at":"2024-12-19 03:27:10","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":362046,"visible":true,"origin":"","legend":"\u003cp\u003emovie s1\u003c/p\u003e","description":"","filename":"movieS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/0a724c5db358c8f0a97bd06e.mp4"},{"id":71833565,"identity":"548b3659-072c-4fcc-ae1b-dd56fe811b03","added_by":"auto","created_at":"2024-12-19 03:35:10","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":336914,"visible":true,"origin":"","legend":"\u003cp\u003emovie s2\u003c/p\u003e","description":"","filename":"movieS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/4b44dce9eb9bc83fea188d3c.mp4"},{"id":71833566,"identity":"478b6dd6-53f4-4f4f-9cd6-262535b4d802","added_by":"auto","created_at":"2024-12-19 03:35:10","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":570607,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"msSI.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5605490/v1/fe39f54f007468138cb28697.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Giant chlorine isotope effect of ion-molecule reaction","fulltext":[{"header":"Full Text","content":"\u003cp\u003eIsotopes carry the messages of molecular creations and transformations. Accordingly, chemical isotope labelling has been a powerful tool for multidisciplinary applications, such as characterizing chemical mechanisms, dating climate change and life origin on the Earth and tracing environmental pollutants\u003csup\u003e1-7\u003c/sup\u003e. Different kinetic effects are exhibited in isotope fractionations and are generally classified into mass-dependent and mass-independent ones\u003csup\u003e4-6\u003c/sup\u003e. The mass-independent effect, mostly ascribed to nuclear spin and magnetic moment, was observed in the chemical reactions under magnetic field\u003csup\u003e6\u003c/sup\u003e. On the contrary, the mass-dependent effect, as a classic content in textbooks,\u0026nbsp;arises from zero-point vibration and quantum tunneling\u003csup\u003e4-7\u003c/sup\u003e, in which hydrogen/deuterium (H/D) isotopologues show the most prominent effect\u003csup\u003e4\u003c/sup\u003e. Heavy-atom isotopic effects, except from the nuclear spin, are usually very weaker or negligible because of the smaller isotopic mass difference ratio (\u0026Delta;\u003cem\u003em/m\u003c/em\u003e). Here we report the extraordinary anomalies of chlorine (\u003csup\u003e35,37\u003c/sup\u003eCl) isotope effect in the dechlorination and dehydrochlorination of \u003cem\u003eiso\u003c/em\u003e-dichloroethylene (H\u003csub\u003e2\u003c/sub\u003eC=CCl\u003csub\u003e2\u003c/sub\u003e) by collisions with argon ion (Ar\u003csup\u003e+\u003c/sup\u003e). The isotope signatures \u0026delta;\u003csup\u003e37\u003c/sup\u003eCl of the backward-scattered C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e (via the dechlorination) and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e (via the dehydrochlorination) yields reach extremely large values, namely, three to four orders higher than the regular \u0026delta;\u003csup\u003e37\u003c/sup\u003eCl values. Since \u003csup\u003e35,37\u003c/sup\u003eCl isotopes have the same nuclear spin and the present dechlorination and dehydrochlorination proceed in a field-free region, this giant isotope effect is irrelevant to the nuclear spins or magnetic moments, thus certainly beyond current models of the heavy-atom isotope effect.\u003c/p\u003e\n\u003cp\u003ePolychlorinated hydrocarbons are widespread toxicants and groundwater contaminants, and the \u0026delta;\u003csup\u003e37\u003c/sup\u003eCl value is a key index of atmospheric and environmental assessments\u003csup\u003e2,7-9\u003c/sup\u003e. However, the Cl-isotope effects of polychlorinated hydrocarbons are diverse and understood insufficiently, primarily due to multiple Cl-isotope fractionation pathways of coexisting isotopologues\u003csup\u003e7-10\u003c/sup\u003e. Three isotopologues of\u003cem\u003e\u0026nbsp;iso\u003c/em\u003e-dichloroethylene, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e (57.4%), C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl\u0026nbsp;(36.7%) and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e (5.9%), coexist as the reagents in the present experiments, where their concentrations are determined with the natural abundance ratio 1 : 3.125 of \u003csup\u003e37\u003c/sup\u003eCl : \u003csup\u003e35\u003c/sup\u003eCl (ref. 10). The isotope ratio of the products can be measured with high-precision mass spectrometry, ever since the pioneering work by Nier and collaborators\u003csup\u003e11\u003c/sup\u003e. For the C-Cl bond cleavage of the monochlorinated compound, the chlorine kinetic isotope effect (KIE) is expressed with the \u003cem\u003eKIE\u003csub\u003eCl\u003c/sub\u003e\u003c/em\u003e value equal to \u003cem\u003ek\u003c/em\u003e\u003csub\u003e35\u003c/sub\u003e/\u003cem\u003ek\u003c/em\u003e\u003csub\u003e37\u003c/sub\u003e, where \u003cem\u003ek\u003c/em\u003e is the Cl-elimination rate constant. The Streitwieser semiclassical limit of \u003cem\u003eKIE\u003csub\u003eCl\u003c/sub\u003e\u003c/em\u003e is 1.013 (ref. 12), considering the frequency difference between C-\u003csup\u003e35\u003c/sup\u003eCl and C-\u003csup\u003e37\u003c/sup\u003eCl bond stretching (a typical mass-dependent effect). For the dechlorination or dehydrochlorination of a dichlorinated compound, the \u0026delta;\u003csup\u003e37\u003c/sup\u003eCl value is determined by,\u003c/p\u003e\n\u003cp\u003e\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{\\delta\\:}{}^{37}Cl=\\left(\\frac{{}^{37}{Cl}_{p}/{}^{35}{Cl}_{p}}{{}^{37}{R}_{std}}-1\\right)\\bullet\\:1000$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e \u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:\\frac{{}^{37}{Cl}_{p}}{{}^{35}{Cl}_{p}}=\\frac{a{\\bullet\\:KIE}_{Cl}+b}{c{\\bullet\\:KIE}_{Cl}+d}$$\u003c/div\u003e \u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere R\u003csub\u003estd\u003c/sub\u003e is the isotope ratio of the standard free ion (\u003csup\u003e37\u003c/sup\u003eR\u003csub\u003estd\u003c/sub\u003e of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e equals 0.32), \u003cem\u003eCl\u003c/em\u003e\u003csub\u003e\u003cem\u003ep\u003c/em\u003e\u003c/sub\u003e corresponds to the ion intensity of Cl-isotopic products measured with the mass spectra and the parameters \u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.426, \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.059, \u003cem\u003ec\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.574, and \u003cem\u003ed\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.941 (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and section 1 of Supplementary Information). The \u003csup\u003e37\u003c/sup\u003eCl-yields are bound to the minor reagents C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e, thus the upper limit of δ\u003csup\u003e37\u003c/sup\u003eCl is about 1319\u0026permil; by assuming that all C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl reagents undergo the \u003csup\u003e35\u003c/sup\u003eCl-elimination after the charge transfer. In the present work, we find that δ\u003csup\u003e37\u003c/sup\u003eCl values are significantly larger than the value of the mass-dependent effect (δ\u003csup\u003e37\u003c/sup\u003eCl \u0026asymp; 7\u0026permil; for the Streitwieser limit) and the upper limit. Mass spectrometry, as a straightforward method to determine the isotope ratio, is frequently frustrated in exploring the dynamics mechanism, thus more powerful experimental techniques are demanded for these extremely large δ\u003csup\u003e37\u003c/sup\u003eCl values.\u003c/p\u003e\u003cp\u003eRecently, many efforts have been put into investigating the H/D isotope effect with state-of-the-art techniques\u003csup\u003e\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e, emphasizing the unexpected slowness of reactions, the intermediate complex, or the scrambling dynamics. Scrambling or roaming is a fascinating mechanism\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, in which two fragments of molecular decomposition have insufficient translational energies to separate and their roaming around each other is followed with an exothermic internal abstraction. An indirect roundabout mechanism was also found in the nucleophilic substitution reaction between Cl\u0026macr; and CH\u003csub\u003e3\u003c/sub\u003eI (ref. 17). The scrambling or roaming mechanism opens a door to unusual reactions and possibly leads to peculiar isotope effects. To the best of our knowledge, such a fundamental issue has never been touched. Using three-dimensional ion velocity map imaging (3D-VMI) \u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e measurements and with the help of \u003cem\u003eab initio\u003c/em\u003e molecular dynamics (AIMD) simulations, we unveil an extremely strong isotope effect (δ\u003csup\u003e37\u003c/sup\u003eCl \u0026asymp; 10\u003csup\u003e5\u003c/sup\u003e \u0026permil;) for the backward-scattered C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e yield of dissociative charge exchange (DCE) reaction Ar\u003csup\u003e+\u003c/sup\u003e + \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e \u0026rarr; Ar\u0026thinsp;+\u0026thinsp;HCl\u0026thinsp;+\u0026thinsp;C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e, and suggest that this remarkable effect is attributed to the H-scrambling and roaming dynamics.\u003c/p\u003e\u003cp\u003eThe 3D-VMI measurements were carried out with our crossed-beam apparatus\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. As shown in Fig.\u0026nbsp;1a, the apparatus consists of a well-confined pulsed Ar\u003csup\u003e+\u003c/sup\u003e ion beam\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, a supersonic molecular beam, an ion VMI optics system, and a delay-line ion detector to realize the 3D imaging. The 3D-VMI technique enables us to simultaneously record the velocity distributions and the time-of-flight (TOF) mass spectra of different ionic yields. The VMI technique is based on the TOF mass spectrometry, but two ions with a small mass difference are generally undistinguishable in the VMI measurement because of the flight-time overlapping of two adjacent ionic Newton spheres\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Fortunately, as shown in Fig.\u0026nbsp;1b, the Cl-isotopologues of the parent ion C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (the charge-exchange-only yield) and the DCE yields (C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e, and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e) are disentangled, partially owing to a proper TOF length (ca. 46.1 cm) of our VMI apparatus\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. At four collision energies in the center-of-mass (c.m.) reaction coordinate (E\u003csub\u003ec.m\u003c/sub\u003e.) 2.58, 3.95, 4.67, and 8.90 eV for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e (E\u003csub\u003ec.m\u003c/sub\u003e. values are slightly different for the minor reagent C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e37\u003c/sup\u003eCl or C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csub\u003e2\u003c/sub\u003e), the productions of the parent ion C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e and the dehydronated yield (C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e) are much lower than those of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e. According to the fitted profiles in the TOF spectra (Fig.\u0026nbsp;1b), we obtain the individual contributions of the Cl-isotopic ions, where each contribution corresponds to the whole Newton sphere of a certain type of these ions. Then, a velocity image can be obtained by slicing the Newton sphere at the equator with a time thickness of 60 ns in the off-line data analyses\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan additionalcitationids=\"CR22 CR23\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eOwing to the low velocities of ionic yields and the large apertures of the VMI electrodes, the ion collection efficiency reaches nearly a hundred percent. As shown in Table S2, we obtain the branching ratios of different channels and the production ratios. With reference to the \u003csup\u003e37\u003c/sup\u003eR\u003csub\u003estd\u003c/sub\u003e values 0.32 of the free ions C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e, we further obtain the δ\u003csup\u003e37\u003c/sup\u003eCl values using Eq.\u0026nbsp;(1) and plot their collision-energy dependences in Fig.\u0026nbsp;1c. Generally, the δ\u003csup\u003e37\u003c/sup\u003eCl values of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e slightly fluctuate around the Streitwieser limit, indicating a normal weak Cl-isotope effect. To our surprise, the extremely large δ\u003csup\u003e37\u003c/sup\u003eCl values, about 10\u003csup\u003e4\u003c/sup\u003e \u0026permil;, are observed for C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e. According to Eq.\u0026nbsp;(2), these δ\u003csup\u003e37\u003c/sup\u003eCl values correspond to 3.33 of the ratio C\u003csub\u003e2\u003c/sub\u003eH\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e/ C\u003csub\u003e2\u003c/sub\u003eH\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e (also see Table S2) which is out of the regular range, namely, from 0.063 as \u003cem\u003eKIE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCl\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;\u0026lt;\u0026thinsp;1 to 0.742 as \u003cem\u003eKIE\u003c/em\u003e\u003csub\u003e\u003cem\u003eCl\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;\u0026gt;\u0026thinsp;1. A question instantly arises: what dynamic process leads to such extraordinary anomalies?\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;2 shows the sliced velocity images of the C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e isotopic yields, while the C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e images are exhibited in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e and not discussed due to the much lower production efficiency. To our surprise again, in Fig.\u0026nbsp;2 we observe the remarkable collision-energy dependences and the significant distribution differences between the \u003csup\u003e35\u003c/sup\u003eCl- and \u003csup\u003e37\u003c/sup\u003eCl-species, implying that the reaction dynamics underneath these images should be more complicated than what we surmised from Fig.\u0026nbsp;1c. Even for the seemingly normal isotope effect of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e (see the middle panel of Fig.\u0026nbsp;1c), the image differences between C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e35\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e also indicate a remarkable dynamic isotope effect. At a given collision energy, for instance, E\u003csub\u003ec.m\u003c/sub\u003e. = 2.58 eV, most \u003csup\u003e35\u003c/sup\u003eCl-species of the C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e or C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e yields are confined in the forward (along the flying direction of the reagent molecule) region and along the collision axis, while a bimodal distribution is observed clearly for the \u003csup\u003e37\u003c/sup\u003eCl-species. In the latter, the backward (along the flying direction of the reagent Ar\u003csup\u003e+\u003c/sup\u003e) distribution is highlighted with a green frame, as shown in Figs.\u0026nbsp;2a and 2e. Furthermore, the backward distribution of C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e or C\u003csub\u003e2\u003c/sub\u003eH\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e observed at the lower collision energy (Figs.\u0026nbsp;2a, 2e) fades down (Fig.\u0026nbsp;2d) or changes to be a little forward (Fig.\u0026nbsp;2h) at the higher collision energy.\u003c/p\u003e\u003cp\u003eTo have insights into the dynamic isotope effect, in Fig.\u0026nbsp;3 we plot the velocity dependences of δ\u003csup\u003e37\u003c/sup\u003eCl for C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e yields at the lowest collision energy. Note that the weighing factors at different velocities are not considered. The δ\u003csup\u003e37\u003c/sup\u003eCl values of the much slower C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e (\u003cem\u003eu\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e ~ 0 m/s) are close to zero and absent in Fig.\u0026nbsp;3a, due to the unusual \u003csup\u003e37\u003c/sup\u003eCl-elimination through a long-lived intermediate. In contrast, a high preference of \u003csup\u003e35\u003c/sup\u003eCl-elimination leads to the large δ\u003csup\u003e37\u003c/sup\u003eCl values. As shown in Fig.\u0026nbsp;3a, the backward C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e ions with velocities larger than 1000 m/s are located out of the yellow-colored region. As mentioned above, this yellow-colored region covers a δ\u003csup\u003e37\u003c/sup\u003eCl range with the assumed upper limit 1319\u0026permil;. Most δ\u003csup\u003e37\u003c/sup\u003eCl values of C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e, as observed in Fig.\u0026nbsp;3b, evidently overtop this yellow-colored range, and exhibit a maximum of 10\u003csup\u003e5\u003c/sup\u003e \u0026permil; for the backward-scattered ions with the velocity about 600 m/s. In the following discussion, we focus on the extraordinary preference of \u003csup\u003e35\u003c/sup\u003eCl-elimination.\u003c/p\u003e\u003cp\u003eTo elucidate the observations, we need to recall basic features about the DCE dynamics of the collisions with Ar\u003csup\u003e+\u003c/sup\u003e (refs. 19\u0026ndash;24): (i) In the large impact-parameter or peripheral collision, the parent and large daughter ionic yields are scattered forward with the velocities close to that of the reagent molecule, and the co-product Ar atom serves as a spectator. (ii) A small impact-parameter or intimate collision facilitates an efficient translational-to-internal energy transformation, then the backward-scattered ions can be produced from the rebounded intermediate. (iii) Due to the long-distance attraction, a randomly oriented molecule can be spatially aligned or oriented during the ion approaching. In the present case, the daughter ions C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e show more delocalized distributions (Fig.\u0026nbsp;2), while the heavier ion C\u003csub\u003e2\u003c/sub\u003eHCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e is located around the molecular reagent position (as shown in Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). The forward C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e could be produced quickly in the large impact-parameter DCE reaction; On the contrary, the backward C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e should be attributed to the relatively slow dissociations of the rebounded \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e formed by the small impact-parameter or head-on collision. In the latter, the \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e structure could be deformed seriously and subsequently dissociate, where the isotopic competition is responsible for the Cl-isotope effect of the backward C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eWe perform the AIMD simulations (Supplementary Information, Figs. S2, S3) to mimic the head-on collisions at the lowest collision energy. Firstly, a comparison between the C-\u003csup\u003e35\u003c/sup\u003eCl and C-\u003csup\u003e37\u003c/sup\u003eCl bond ruptures in two representative trajectories is described in Fig.\u0026nbsp;4a. The C-\u003csup\u003e37\u003c/sup\u003eCl bond cleavage lags much behind the C-\u003csup\u003e35\u003c/sup\u003eCl bond, leading to the \u003csup\u003e35\u003c/sup\u003eCl-elimination preference; then C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e survives via the more active C-\u003csup\u003e37\u003c/sup\u003eCl stretching motion. This is in line with the normal mass-dependent isotope effect: the C-\u003csup\u003e37\u003c/sup\u003eCl bond energy is a little higher than the C-\u003csup\u003e35\u003c/sup\u003eCl bond, due to the lower zero-point vibrational energy of the former; the vibrational-state density of the C-\u003csup\u003e37\u003c/sup\u003eCl stretching is higher than that of the C-\u003csup\u003e35\u003c/sup\u003eCl stretching, because of the smaller vibrational-state energy interval of the C-\u003csup\u003e37\u003c/sup\u003eCl stretching.\u003c/p\u003e\u003cp\u003eTwo representative trajectories of the dehydrochlorination are plotted in Fig.\u0026nbsp;4b. One can find the H atom scrambling or roaming before the \u003csup\u003e35\u003c/sup\u003eCl-abstraction. It is noted that, in the dissociative photoionization, Cl-atom scrambling in the vicinity of the two-pathway crossing was proposed by scanning the C-Cl and C-H bond lengths on the potential energy surface\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. In the present on-the-fly AIMD results, the dynamic processes (Fig. S3) are roughly classified into the fast (case \u003cem\u003ea\u003c/em\u003e) and slow (case \u003cem\u003eb\u003c/em\u003e) types. In case \u003cem\u003ea\u003c/em\u003e (also see movie S1), the H atom at the \u003csup\u003e35\u003c/sup\u003eCl side scrambles quickly before the \u003csup\u003e35\u003c/sup\u003eCl-abstraction. In case \u003cem\u003eb\u003c/em\u003e (also see movie S2), the H atom at the \u003csup\u003e37\u003c/sup\u003eCl side roams from -C\u003csub\u003eβ\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003e to -C\u003csub\u003eα\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e, an intermediate Cl\u003csub\u003e2\u003c/sub\u003eC\u003csub\u003eα\u003c/sub\u003eH-C\u003csub\u003eβ\u003c/sub\u003eH\u003csup\u003e+\u003c/sup\u003e is formed temporarily, and then this H atom transfers back to the C\u003csub\u003eβ\u003c/sub\u003e end and goes to the \u003csup\u003e35\u003c/sup\u003eCl side via a roundabout route, finally abstracting the \u003csup\u003e35\u003c/sup\u003eCl atom.\u003c/p\u003e\u003cp\u003eThe dynamic processes to produce C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csup\u003e+\u003c/sup\u003e and C\u003csub\u003e2\u003c/sub\u003eHCl\u003csup\u003e+\u003c/sup\u003e could start from \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{\\sim}{\\text{F}}\\)\u003c/span\u003e\u003c/span\u003e state (the sixth valence-exited state) of \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (ref. 26) after the prompt charge transfer from Ar\u003csup\u003e+\u003c/sup\u003e to \u003cem\u003eiso\u003c/em\u003e-C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eCl, but those AIMD computations are unaffordable due to state-to-state nonadiabatic propagations within multiple degrees of nuclear motion freedom. Some limitations of the present simulations are also addressed in section 3 of Supplementary Information. Nevertheless, the \u003csup\u003e35\u003c/sup\u003eCl-elimination assisted with the H-atom scrambling or roaming is a heuristic model, in which the Cl-isotope effect can be magnified with more than one thousand times. Our finding paves a way to a piece of virgin land of heavy-atom isotope effects. Moreover, this work potentially advances the isotope fractionation techniques and provokes to refine the heavy-atom isotope labelling protocols.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are included in the paper, and Supplementary Information and Supplementary Videos are available online or from the corresponding author upon the request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank supported by National Natural Science Foundation of China (22233004) and the Innovation Program for Quantum Science and Technology (2021ZD0303303). The numerical calculations were done in the Supercomputing Center of USTC. We appreciate Prof. Jun Jiang\u0026rsquo;s help on the computational source and the valuable discussions with Prof. Yi Luo.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eYZ and JH carried out the experiments. YZ did the theoretical simulations. JCX and CXW participated in the calculations and experimental operations, respectively. YZ, JH and SXT performed the data analyses. YZ, JH and SXT contributed to drafting the manuscript. JH and SXT conceived the project, SXT supervised this work.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u0026nbsp;\u003c/strong\u003eThe experimental and AIMD simulation methods and additional results, supplementary videos) available at\u0026hellip;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence and requests for materials\u003c/strong\u003e should be addressed to S.X.T.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGriffiths H (1998) Stable isotopes. Integration of Biological, Ecological and Geochemical Processes. 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An experimental and quantum chemical study. J Phys Commun 1:055030\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5605490/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5605490/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIsotope substitution profoundly influences chemical reactions, signifying different reaction rates due to mass-related nuclear quantum effects. Due to the smaller mass-difference ratio, heavy-atom isotope effect is usually much weaker than the hydrogen/deuterium effect, which has been the underlying principle for chemical isotope labelling, a prevailing technique of environmental assessments. Here we report a giant chlorine (\u003csup\u003e35,37\u003c/sup\u003eCl) isotope effect of the collisional reactions between \u003cem\u003eiso\u003c/em\u003e-dichloroethylene (naturally comprising \u003csup\u003e35,37\u003c/sup\u003eCl-isotopologues) and argon ion. As a grave challenge to conventional understandings, we find that the isotopic signature δ\u003csup\u003e37\u003c/sup\u003eCl of the dehydrochlorination channel is one thousand times larger than the regular values, namely, an extraordinary priority of the product C\u003csub\u003e2\u003c/sub\u003eH\u003csup\u003e37\u003c/sup\u003eCl\u003csup\u003e+\u003c/sup\u003e. Hydrogen-atom scrambling and roaming assisted \u003csup\u003e35\u003c/sup\u003eCl-elimination mechanisms are proposed for this unprecedentedly strong isotope effect. Our finding adds a new dimension of isotope effects and enlightens related methodological renovations of environmental assessment.\u003c/p\u003e","manuscriptTitle":"Giant chlorine isotope effect of ion-molecule reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-19 03:27:05","doi":"10.21203/rs.3.rs-5605490/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c9d3e5e1-ce65-43c8-8fa1-3bf92c537de3","owner":[],"postedDate":"December 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":41773265,"name":"Physical sciences/Chemistry/Physical chemistry/Reaction kinetics and dynamics"},{"id":41773266,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Environmental monitoring"}],"tags":[],"updatedAt":"2025-02-03T12:21:12+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-19 03:27:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5605490","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5605490","identity":"rs-5605490","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}