Theoretical Study on the Atmospheric Reaction of HS with HO2: Mechanism and Rate Constants of the Major Channel

mechanism for the biradical reaction of HS with HO2 is investigated at the CCSD(T)/6-311++ G(3df,2pd)//B3LYP/6-311+G(2df,2p) level on both the singlet and triplet potential energy surfaces, along with rate constant calculations of the major channel. The results show that there are eight reaction channels involved in the HS + HO2 reaction system. The major channel R1 of the title reaction occurs on the triplet potential energy surfaces, and includes two pathways: Path 1 (R -> (3)IM1 -> (3)TS1 -> P1(O-3(2) + H2S)) and Path la (R -> (3)M1a -> P1(O-3(2)+ H2S)). The rate constants k(TST), k(CVT), and k(CVT/SCT) of Paths 1 and 1a for Channel R1 were evaluated using classical transition state theory (TST) and the canonical variational transition state theory (CVT), in which the small -curvature tunneling correction was included. The calculated results show that K-TST. K-CVT and K-CVT/SCT of these two pathways decrease with rising temperature within the temperature range of 200-800 K. The variational effect was not negligible in the entire process of Path 1 and Path 1 a, at the same time, the tunneling effect was considerable at lower temperature. The fitted three-parameter expressions of k(CVT/SCT) for Paths 1 and 1a are k(CVT/SCT)(200-800 K) = 1.54 x 10(-5)T(-270) exp(1154/T) cm(3) molecule(-1).(s-1) and k1a(CVT/SCT) (200-800 K) = 5.82 x 10-57-1-54exp(1388/T) cm3- molecule -1-s', respectively.