Nuclear quantum effect and H/D isotope effect on Cl· + (H2O)n → HCl + OH·(H2O)n−1 (n = 1–3) reactions

Abstract

Cl· + (H₂O)_n → HCl + OH·(H₂O)_n−1 (n = 1–3) reactions are fundamental and important ones in atmospheric chemistry. In this study, we focused on the nuclear quantum effect (NQE) of the hydrogen nucleus on these reactions with the aid of the multicomponent quantum mechanics (MC_QM) method, which can directly take account of NQE of light nuclei. Our study reveals that the NQE of the hydrogen nucleus lowers the activation barriers of the reactions and enhances the catalytic effects of second and third water molecules. In particular, we find that (i) the NQE of the proton removes the activation barrier of the reverse reaction of HCl + OH· → Cl· + H₂O, and (ii) the catalytic effect of the third water molecule appears in only our MC_QM calculation. We also analyze the H/D isotope effects on these reactions by using the MC_QM method.