Theoretical research on the multi-channel reaction mechanism and kinetics of HNCS with OH anions

Abstract

publicado na web em 15/08/2017We presented a theoretical study on the detailed reaction mechanism and kinetics of the HNCS molecule with the OH -. The barrierless minimum energy path and the most favorable entrance channel have been determined by study the thermodynamic and kinetic characters of the channel with low energy barrier. The B3LYP/6-311++G** method was employed for all the geometrical optimizations and a multi-level extrapolation method based on the G3 energies was employed for further energy refinements. In addition, the analysis of the combining interaction between hydroxide ion and HNCS was performed by natural bond orbitals (NBO) analysis. The calculation results indicated that the reaction of OH -with HNCS had four channels, and the channel of H-atom in HNCS direct extraction to OH -(OH -+HNCS→IM1→TS3→IM4→P2(SCN -+H 2 O)) in singlet state was the main channel with the low potential energy and high equilibrium constant and reaction rate constant. SCN -and H 2 O were main products.Keywords: hydroxide ion; isothiocyanic acid; mechanism; equilibrium constant INTRODUCTIONThe problem of the severe air pollution in developing countries has caused wide public concern over the recent years, heavy power plant smoke and car emissions, mainly in the form of sulfate, organic, nitric acid and particles, have always been a threat to the global public health. In the meanwhile, as important intermediates of sulfur-containing fuel combustion process, HNCS and its derived free radical NCS can participate in the process of removal the toxic NO 4 compounds from rapid combustion exhaust gas too. [1][2][3][4][5][6] Due to its important role, the theoretical study on the reaction mechanism of HNCS with small molecules by quantum chemistry calculation also become the focus of the chemical workers' research. [7][8][9][10][11][12][13][14][15][16][17][18][19] Because its oxidation ability is very strong, hydroxide ion (OH -) is one of the key intermediates in the interstellar environment and a large number of combustion reaction, not only represents a very important role that OH -can oxidized volatile organic compounds in the troposphere gas, 20 but also plays an important role in atmospheric chemistry where it is the primary process responsible for removal of the H 2 CO pollutant.21-25 Molecular anions play an important role in the chemistry of the interstellar medium, of carbon stars , and the Earth' s ionosphere. One such species is the hydroxide ion. Madura and Jorgensen applied ab initio calculation to discuss the addition of hydroxyl anion to the aldehydic carbon atom. 26 Herein, we used the density functional theory (DFT) to explore the reaction mechanism of OH -with HNCS, We hope our work might provide theoretical guidance to control NO x substance-related air pollution effectively. CALCULATION METHODSAll calculations were performed with the Gaussian 03 package. 27 The geometries of reactants, intermediates, transition states and products were optimized at the DFT-B3LYP/6-311++G** level. 28-31The harmonic vibration ...