Structures and stabilities of HPS₂ isomers

The potential energy surface of HPS₂ system containing nine isomers and fifteen transition states is obtained at MP2/6-311++G(d, p) and QCISD(t)/6-311++G(3df,2p)(single-point) levels. On the potential energy surface, the lowest-lying trans-HSPS(E1) is found to be thermodynamically the most stable isomer followed by cis-HSPS(E2) and HP(S)S(C_2v, E3) at 3.43 and 14.17 kj/mol, respectively. The computed results show that species E1, E2, E3, stereo HP(S)S(C_S, E4) with PSS three-membered ring, isomers trans-HPSS(E5) and cis-HPSS(E6) which coexist with E4 are kinetic stable isomers. The products E6 and E5 in the reaction of HP with S₂ can be isomerized into higher kinetic stable isomer E4 with 65.75 and 71.73 kj/mol reaction barrier height, respectively. The predicated results may correct the possible inaccurate conclusion in which the product was experimentally assigned as isomer cis-HPSS(E6).