Can (H2O) n (n = 1–2) as effective catalysts in the CH2OO + H2S reaction under tropospheric conditions?

Abstract

The addition reaction of CH2OO + H2S → HSCH2OOH without and with catalyst X (X = H2O and (H2O)2) has been investigated by CCSD(T)-F12a/VTZ-F12//B3LYP/aug-cc-pVTZ method and canonical variational transition state theory with small curvature tunneling correction. When H2O was introduced in the CH2OO + H2S reaction, it not only acts as a catalyst for producing HSCH2OOH, but also plays as a reactant to forming HOCH2OOH. The formation channel of HSCH2OOH is more important than the formation channel of HOCH2OOH with its calculated rate constant larger by 11.0–43.2 times within the temperature 280–320 K. Then, (H2O)2 catalysed CH2OO + H2S → HSCH2OOH reaction has been taken into account with its rate lower 1.9–4.2 times than the reaction of CH2OO + H2S → HSCH2OOH with water. Also, CH2OO + H2S with H2O cannot compete with the CH2OO + H2S reaction without water. This is different from CH2OO + (H2O)2 reaction, which is about 4 orders of magnitude larger than the rate constant for CH2OO + H2O reaction. Such discrepancy is possible because C(CH2OO)···O(H2O) interaction has been enhanced more obviously by H2O as compared to that of C(CH2OO)···O(H2S) interaction.