Cyanopolyynes in the Interstellar Medium: Obtaining Rotational Constants in Silico

This work theoretically investigates cyanopolyynes (with the general molecular formula HCnN, n = 3, 5, 7…), which are chemical species detected in various regions of space, including the interstellar medium and Titan’s atmosphere (Saturn’s largest moon). These molecules are relevant, for example, in astrochemistry and molecular electronics. Using computational quantum chemistry methods at the DFT/B3LYP/6-311G(3df,3pd) theory level with ORCA software, we calculated rotational constants and dipole moments, which are essential for their detection in the ISM by rotational spectroscopy. The study proposes two correlation models: the ”Dipole_Model”, which correlates the rotational constant with the dipole moment, and the ”Mass_Model”, which correlates the rotational constant with the molecular mass. Both are consistent with the experimental data, however, the “Mass_Model” proved to be more accurate for larger molecules, suggesting that molecular mass is a more reliable parameter in predicting rotational constants and the consequent detection of new species in space.