A Gaussian-2 ab initio study of [C2H5S](+) ions: II. fragmentation and CH3SCH2+ and CH2CHSH2+ revisited

Gaussian-2 ab initio method was performed to examine the five modes of unim olecular dissociation of CH3SCH2+ (1(+)) and CH2CHSH2+ (5(+)): 1(+) --> CH3 + H2CS+ (1); 1(+) --> CH + H2CS (2); 1(+) --> CH4 + HCS+ (3); 5(+) --> H2S + [C2H3](+) (4); and 5(+) --> H3S+ + C2H2 (5). Both reactions 1 and 2, wit h endothermicities 359 and 395 kJ mol(-1) respectively, proceed without a r everse barrier. Loss of CH4 from 1(+) (reaction 3) proceeds via a transitio n state resembling an ion-radical complex CH3/ H2CS+. The elimination react ion has an energy barrier of 332 kJ mol(-1). Loss of H2S from 5(+) (reactio n 4) initially proceeds through either cleavage of the C-S bond or formatio n of the ion-molecule complex H2S/[C2H3](+) (8(+)/9(+)), followed by dissoc iation of the complex. The endothermicity of reaction 3 is calculated to be 245-261 kJ mol(-1). Reaction 5, the lowest energy process among the dissoc iation pathways studied in this work, proceeds via intermediates 9(+) and H 3S+/C2H2 (10(+)). Its rate-determining step 5(+) --> 9(+) has an energy bar rier of 220 kJ mol(-1). (C) 1999 Elsevier Science B.V. All rights reserved.