Rearrangement and fragmentation pathways of [C(3)H(7)Z](+) ions (Z = NH and S): are ion-neutral complexes important?

High level ab initio calculations at the G2(ZPE = MP2) level have been used to characterize the potential energy surfaces for rearrangement/fragmentat ion of various [C3H8N](+) and [C3H8S](+) isomers. In contrast to the behavi or in the corresponding [C3H7O](+) system, it is found that ion-neutral com plexes are only of minor:importance in determining the fragmentation ;chara cteristics. Either dissociation of such complexes occurs too fast due to a large barrier to their formation ([C3H8N](+) system), or alternative lower- energy rearrangement routes that do not involve ion-neutral complexes are a vailable ([C3H7S](+) system). Calculated thermochemical quantities such as heats of formation and reaction barriers are found to be in reasonable agre ement with experimental results. Metastable ion product abundances and resu lts of both deuterium- and C-13-labeling experiments are rationalized in te rms of the calculated potential energy surfaces and rate constants obtained using Rice-Ramsperger-Kassel-Marcus theory. (Int J Mass Spectrom 194 (2000 ) 181-196) (C) 2000 Elsevier Science B.V.