The DPT B3LYP calculations predict isotropic proton hyperfine coupling constant A (H) value of 127. 4 MHz for the HCS radical, in excellent agreement with the recently reported ex- perimental value of 127.427 MHz. The B3LYP calculations confirm the experimental fact that the A (H) value of HCS is much smaller than the A (H) values of HCO, HSiS, and HSiO, for which we present a simple explanation on the basis of the analysis of spin densities.
The mechanisms of the C(3P)+H 2SHCS+H and C(3P)+H 2S → HSC+H reactions have been studied at the UMP2/631G(d,p),UMP2/6311G(d,p),and G2 levels,and six transition states and three intermediates have been located along the reaction paths. The predicted path for the C(3P)+H 2SHCS+H reaction is:C(3P)+H 2SIM1TS1IM2TS4HCS+H,in line with the reaction process suggested by Lee et al. [1] in which only the intermediates were given. Our energetic results indicate that the C(3P)+H 2SHCS+H reaction is more favorable than the C(3P)+H 2SHSC+H reaction,in agreement with experiment.
The mechanisms of the CH2＋ O2→ H2O＋ CO and CH2＋ O2→ H2＋ CO2 reactions have been studied by performing ab initio CAS(8,8)/6-31G(d,p) calculations, and five intermediates(IMn) and eight transitions(TSn) have been located along the reaction paths. The predicted path for the CH2＋ O2→ H2O＋ CO is: CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS5→ H2O＋ CO. For the CH2＋ O2→ H2＋ CO2 reaction, there are two paths: (i) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS6→ H2＋ CO2 and (ii) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS7→ IM4b→ TS8→ H2＋ CO2, with the latter path more favorable energetically.
