High-level theoretical study of the hydrogen abstraction reaction H2S + O2 = SH + HO2 and prediction of the rate constants

Publication date: 1 May 2019Source: Computational and Theoretical Chemistry, Volume 1155Author(s): Quan-De Wang, Mao-Mao Sun, Jin-Hu LiangAbstractHydrogen abstraction reaction of hydrogen sulfide (H2S) by molecule oxygen (O2) forming hydroperoxyl radical (HO2) and hydrosulfide radical (SH) is very important for both atmospheric and combustion chemistry. This work reports a systematic theoretical study on this reaction using a combination of high-level quantum chemistry methods and chemical kinetic theory. Geometry optimizations for all species are performed at QCISD/cc-pVQZ level of theory. The energies for minima and transition state are computed using both single- and multi-reference ab initio methods. It is found that the transition state of this reaction exhibits significant multi-reference nature based on 〈S2〉 and T1 diagnostic during CCSD(T) calculations. The predicted reaction barrier from high-level multi-reference CASPT2(20e,13o)/aug-cc-pVTZ method is higher than those from CCSD(T) and W1BD methods by 6–7 kcal mol−1. Reaction energy barriers from a series of DFT methods also show large deviations compared with both single- and multi-reference methods. Thermal rate constants are calculated over a temperature range from 300 to 2500 K by employing canonical transition state theory with Eckart tunneling correction and the treatment of torsional mode. This work provides accurate rate constants for this reaction and fundamental benchmark results for H/O/S rea...

Source: Computational and Theoretical Chemistry - March 28, 2019 Category: Chemistry Source Type: research