Effect of a single water molecule on the formations of H₂O₂ + ClO from HO₂ + HOCl reaction under tropospheric conditions

Abstract

In this work, four different channels, represented by H2O•••HO2 + HOCl, HO2•••H2O + HOCl, H2O•••HOCl + HO2 and HOCl•••H2O + HO2 have been analysed for water-catalysed formations of H2O2 + ClO to gain insight into the potential impact of the reaction in the atmosphere. The results at the CCSD(T)/aug-cc-pVTZ//MP2/6-311+G(2df,2p) level show that the H2O•••HO2 + HOCl reaction is kinetically the most favourable channel among the four channels. Compared to the channel of H2O2 + ClO formations without water vapour, the effective rate constant of H2O•••HO2 + HOCl reaction is estimated to be faster than the naked reaction by 2–3 orders of magnitude, indicating that the single water molecule in the H2O•••HO2 + HOCl channel exhibits a positive catalytic effect on enhancing the rate of H2O2 + ClO formations. Meanwhile, it is interesting that the transfer process between H2O•••HOCl + HO2 and H2O•••HO2 + HOCl has an activation energy of 0.6 kcal⋅mol−1 and can occur easily under tropospheric conditions.