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摘要
A detailed theoretical survey of the potential energy surface (PES) for the reaction CH3S with HCS in gas phase is carried out at the QCISD(t)/6-311++G(d,p)//MPW1PW91/6-311G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the title reaction are calculated at the MPW1PW91/6-311G(d,p) level. More accurate energy information is provided by single-point calculations at QCISD(t)/6-311 + + G(d,p) level. Relationships of reactants, intermediates, transition states and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. 8 intermediates and 9 transition states are located and a variety of possible reaction pathways are probed. The association of CH3S with HCS is found to be a barrierless process. Firstly it forms the energy-rich adducts a (five-member ring-type structure) or c (chain structure) through the weak S center dot center dot center dot S bond. Then, from adducts a and c, the main product P1 (2CH(2)S) can be produced, as well as secondary important products P2 (CH3SH+CS), P3 (CH4+ CS2) and P4 [CH2(SH)CSH] via the different channels, i.e. hydrogen shift, dissociation and isomerizazion. The reaction pathway leading to the major product 2CH(2)S is as follows: R-->a-->TSa/b-->b-->P1. The rate constant of step a-TSa/b-->b is k(1)(CTT/SCT)=1.75X10(10)T(0.65) exp(-907.6/T) s(-1) by means of small-curvature tunneling correction in the temperature range of 200 similar to 2000 K. By the analysis of-the potential energy surface, we can draw the conclusion that all the channels are exothermic reactions and the reaction heat of generating P1 is - 165.55 kJ.mol(-1).
