The reaction mechanisms of the ground state 1Σ+ of YS+ with oxygen-transfer reagent: YS+ +COS→YO+ +CS2 in the gas phase has been studied by ab initio methods. It is found that the reaction proceeds via two four-center transition states (TS1 and TS2) with a cyclic complex (b) locating between them on the reaction potential surface. The activation barriers of the two transition state are both negatively valued by -7.6 kcal/mol at MP4 (SDTQ)/6-31+G*//MP2/6-31+G* level plus ZPE relative to the reactants. The collision rate coefficient of the reactants should be the main factor limiting the reaction rate. The similarities and differences between YS+ and ScS+ for this type reaction were also discussed.

The reaction mechanisms of the 1Σ+ ground state of YS+ with oxygen-transfer reagent: YS+ +CO2→YO+ +COS in the gas phase has been studied by using density functional theory (DFT). It is found that the reaction proceeds via two four-center transition states (TS1 and TS2) with a cyclic complex (b) locating between them on the reaction potential surface. The activation barriers of the two transition state are -8.3 and 2.1 kcal/mol, respectively, at B3LYP/6-31+G* level plus ZPE relative to the reactants. The second reaction step via transition state TS2 should be the rate-determining reaction step. The similarities and differences between YS+ and ScS+ for this type reaction were also discussed.

The reaction mechanism of the ground state 2∆ of TiS+ with oxygen-transfer reagent: TiS+ +H2O→TiO+ +H2S in the gas phase has been proposed and investigated by ab initio methods with 6-31G** basis set for non-metal atoms and the effective core potentials of Lanl2dz for Ti. The reaction is proceeding via two steps with seven stationary points (reactants, three intermediate complexes: (a), (b) and (c) two transition states: TS1 and TS2, and products) on the reaction potential surface which involved two 1, 3-hydrogen shift reactions from oxygen atom to sulfur atom via a four-center transition state. The activation barriers of the two transition states are -54.0 and -65.1 kcal/mol, respectively, at MP4 (SDTQ)/6-31G**//MP2/6-31G** level plus zero-point energy relative to the reactants, which indicates that cationic titanium sulfide is favorable to this type of reaction and the collision rate of the reactants forming the complex (a) should be the main factor that determines the reaction rate.

The reaction mechanism of the ground state 1Σ+ of ScS+ with oxygen-transfer reagent: ScS+ +H2O→+ScO+ +H2S in the gas phase has been proposed and investigated by ab initio methods with 6-31G** basis set for non-metal atoms and the ECPs of Lan 12dz for Sc. The reaction is proceeding via two steps with seven stationary points (reactants, three intermediate complexes: (Ⅰ), (Ⅱ) and (Ⅲ), two transition states: TS1 and TS2, and products) on the reaction suface which involved two 1, 3-hydrogen-shift reactions from oxygen atom to sulfur atom via a four-center transition state, respectively. The activation energies of the two steps are 25.3 and 30.2 kcal mol-1, respectively, at MP4 (SDTQ)/6-31G**//MP2/6-31G** level plus zero-point energy, which indicates that the second reaction step is the rate-determining step and the theoretical rate constants based on the transition state theory (TST) with Wigner and Eckart tunneling correction are 2.45 and 42.02 (in 10-10 s-1), respectively, for the forward reaction and 0.003 and 0.048 (in 10-10 s-1) for the reverse reaction.

The reaction mechanisms of the 1Σ+ ground state of ScS+ with oxygen-transfer reagent: ScS+ +COS→ScO+ +CS2 in the gas phase has been studied by using ab initio methods. It is found that the reaction proceeds via two four-center transition states (TS1 and TS2) with a cyclic complex (b) located between them on the reaction potential surface. The first reaction step proceeding via TS1 is rate limiting and the activation barriers are 31.5 and 6.4 kcal/mol at MP4 (SDTQ)/6-31+G*//MP2/6-31+G* level plus ZPE, relative to the intermediate complex (a) and the reactants, respectively.

The reaction mechanisms of the title reaction have been studied by using density functional theory (DFT) and Møller–Plesset perturbation theory (MP2). It is found that the reaction proceeds via two four-center transition states (TS1 and TS2) with a cyclic complex (b) locating between them on the reaction potential surface. The activation barriers of the two transition states are both negatively valued by -8.6 and -2.6 kcal/mol, respectively, at B3LYP/6-311+G level. Another reaction channel: ScS+ +CO2→ScOS+ +CO was also investigated and its activation barrier is much higher (50.2 kcal/mol) which is in line with the experimental observation.

The reaction mechanism of the ground state 1Σ+ of LaS+ with oxygen-transfer reagent: LaS+ +H2O→LaO+ +H2S in the gas phase has been proposed and investigated by ab initio methods. The reaction is proceeding via two 1,3-hydrogen-shift reactions from oxygen atom to sulfur atom (via TS1 and TS2). The activation energies of two steps are 20.8 and 29.5 kcal/mol, respectively, at MP4 (SDTQ)/6-31G**//MP2/6-31G** level plus zero-point energy relative to their corresponding intermediate reactants. But TS1 locates higher in energy that TS2 by only 1.8 kcal/mol on the reaction path. The periodic trends of Sc, Y and La for this type of reaction were also discussed.

The reaction mechanisms of the 1Σ+ ground state of LaS+ with oxygen-transfer reagent: LaS+ +COS→LaO+ +CS2 in the gas phase has been studied by ab initio methods. It is found that the reaction proceeds via two four-center transition states (TS1 and TS2) with a cyclic complex (b) locating between them on the reaction potential surface. The activation barriers of the two transition state are 3.4 kcal/mol at MP4 (SDTQ)/6-31+ G*//MP2/6-31+ G* level plus ZPE relative to the reactants. The similarities and differences among ScS+, YS+ and LaS+ for this type reaction were also discussed.

The mechanisms of the two possible unimolecular competing reactions occurring during the pyrolysis of dithioformic acid have been proposed and investigated by ab initio calculations with a variety of basis sets. The effects of valence electron correlation were included by M

The mechanisms of the possible unimolecular reactions occurring during the pyrolysis of the four tautomers (two conformers of thiol-and two conformers of thiono-) of monothioformic acid have been proposed and investigated by ab initio methods with STO-3G and 6-31G** basis sets. The effects of valence electron correlation were included by M