On the kinetic stability of the SH3X species with X=F, Cl

Abstract

Portions of the [S, H3, X] (X=F, Cl) potential energy surfaces (PESs) were explored using the RHF, MP2, and QCISD(T) methods with emphasis on H2 and HX eliminations, SH3X→SHX+H2 and SH3X→SH2+HX, respectively. Upon the halogen X substitution, the most favorable decomposition pathway of SH4 went over to HX elimination, proceeding with a very low activation barrier of 6.9 (X=F) and 1.3 (X=Cl) kcal/mol. Moreover, the transition states (TSs) for H2 elimination from SH3X resembled the less favorable homopolar TS of SH4. Upon the X=F substitution, the barrier to H2 loss of SH4 was calculated to increase from 19.5 to 21.5 kcal/mol. For X=Cl, only the indirect H2 elimination path via the SH2+HCl→SHCl+H2 exchange was found. The hydrogen-exchange reaction SH2+HX→SH2+HX was predicted to occur through formation of the hydrogen-bonded complex XHSH2 and with a relatively high barrier of 43.5 (X=F) and 38.5 (X=Cl) kcal/mol. FHSH2 and ClHSH2 were found to be the lowest energy species on the [S, H3, F] and [S, H3, Cl] PESs, lying 53.4 and 44.7 kcal/mol below SH3F and SH3Cl, respectively. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 37–43, 1999