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.