Significant role of secondary electrons in the formation of a multi-body chemical species spur produced by water radiolysis

Abstract Scientific insights into water photolysis and radiolysis are essential for estimating the direct and indirect effects of deoxyribonucleic acid (DNA) damage. Secondary electrons from radiolysis intricately associated with both effects. Herein, we simulate the femtosecond (1 × 10− 15 s) dynamics of secondary electrons ejected by energy depositions of 20−30 eV into water via high-energy electron transport using a time-dependent first-principles simulation code. The simulation results present the earliest formation mechanism of an unclear multi-body chemical species spur when secondary electrons induce further ionisations or electronic excitations. The formation involves electron–water collisions, i.e. ionisation, electronic excitation, molecular excitation and elastic scattering. Our simulation results indicate that (1) most secondary electrons delocalise to ~ 12 nm, and multiple collisions are sometimes induced in a water molecule at 22 eV deposition energy. (2) The secondary electrons begin to induce diffuse band excitation of water around a few nm from the initial energy deposition site and delocalise to ~ 8 nm at deposition energies ~ 25 eV. (3) The secondary electron can cause one additional ionisation or electronic excitation at deposition energies > 30 eV, forming a multi-body chemical species spur. Thus, we propose that the type and density of chemical species produced by water radiolysis strongly depend on the deposition energy. These findings provide significant chemical and biological insights into the formation of multiple DNA damage, believed to induce the latter biological effects, such as cell death, mutation or carcinogenesis.