Thermodynamic and kinetic investigations on the reaction of methanethiol with oxygen atom

1411-1415The mechanism of the reaction of CH3SH+O has been studied by employing density functional theory at the B3LYP/6-311++G** level. Two reaction channels, viz., the O-attack of the H atom of -SH group (R1), and, the O-attack of the C atom of –CH3 group (R2) have been found. Optimized geometries, frequencies and energies of the stationary points are calculated at the B3LYP/6-311++G** level of theory. The thermodynamic data and the equilibrium constants of the two channels for CH3SH+O reaction are calculated using the statistic theory at 200-2000 K. On the basis of Eyring transition state theory with Wigner correction, the activation parameters, the rate constants and frequency factors of the two reaction channels are obtained in the range of 200 to 2000 K. The results show that both channels of the reaction CH3SH+O are spontaneous and exothermic and that the entropy decreases in the range 200-2000 K. Both channels of this reaction are thermodynamically dominant at low temperatures and kinetically favored at higher temperatures. Although the two channels are competitive over the entire temperature range, channel I (R1) has both thermodynamic and kinetic advantage over channel II (R2), and is the major reaction pathway of CH3SH+O at 200-2000 K