The mechanism and kinetics of the gas-phase reactions of OH radicals with O,O-diethyl methylphosphonothioate, (C2H5O)2P(S)CH3: Theoretical investigations

Abstract

In this research, the kinetics of bimolecular reaction of O,O-diethyl methylphosphonothioate (DEMPT) with OH radical is investigated theoretically. First, the mechanism of the reaction of OH radical with DEMPT is explored some by well-tested density functional methods. Next, the rate constants for different reaction pathways are calculated by statistical rate theories. The results are compared with available experimental data. The present calculations reveal that in the most favorable reaction pathway, the reaction proceed through a relatively deep complex due to the hemi-bond between OH radical and sulphur atom of DEMPT leading to the product (C2H5O)(OH)P(S)CH3+C2H5O. Other product channels have minor contribution to overall reaction rate. The present theoretical rate coefficients are in accord with the available empirical data. Based on the predicted rate coefficients, the tropospheric lifetime of DEMPT is estimated to be about 50 min.