A Gaussian-2 ab initio study of CH2SH, CH2S−, CH3S−, CH2SH−, CH3SH−, CH3+, and CH3SH+

Abstract

Using the Gaussian-2 (G2) theoretical procedure, we have examined the molecular structures and total energies for CH2SH, CH2S−, CH3S−, CH2SH−, CH3SH−, CH3+, and CH3SH+. Contrary to the relative stabilities of CH3S+(C3v;3A2) and CH2SH+(Cs;1A′), the methylthio radical CH3S(Cs;2A′) and the methylthio anion CH3S−(C3v;1A1) are predicted to be more stable than the mercaptomethyl radical CH2SH(C1;2A) and the mercaptomethyl anion CH2SH−(Cs;1A′) by 9.2 and 38.0 kcal/mol, respectively. The CH2SH−(Cs;1A′) anion may exist in the cis configuration or the less stable trans structure. Combined with the results of previous G2 calculations, this calculation yields predictions for the adiabatic ionization energies (IE) of CH3 (9.79 eV), CH2SH (7.41 eV), and CH3SH (9.55 eV), which are in accord with the experimental IEs of 9.84 eV for CH3, 7.536±0.003 eV for CH2SH, and 9.440 eV for CH3SH. The G2 values for the adiabatic electron affinities (EA) of CH2S, CH2SH to trans-CH2SH−(Cs;1A′), CH2SH to cis-CH2SH−(Cs;1A′), and CH3S are 0.38, 0.52, 0.61, and 1.86 eV, respectively. The EA(G2)’s of CH2S and CH3S also agree with the respective experimental values of 0.465±0.023, and 1.861±0.004 eV. We find that CH3SH− is unstable with respect to the electron detachment channel CH3SH+e−.