Rearrangement and fragmentation pathways of [C3H7Z]+ ions (Z = NH and S): are ion-neutral complexes important?

Abstract

High level ab initio calculations at the G2(ZPE = MP2) level have been used to characterize the potential energy surfaces for rearrangement/fragmentation of various [C3H8N]+ and [C3H7S]+ isomers. In contrast to the behavior in the corresponding [C3H7O]+ system, it is found that ion-neutral complexes are only of minor importance in determining the fragmentation characteristics. 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 available ([C3H7S]+ system). Calculated thermochemical quantities such as heats of formation and reaction barriers are found to be in reasonable agreement with experimental results. Metastable ion product abundances and results of both deuterium- and 13C-labeling experiments are rationalized in terms of the calculated potential energy surfaces and rate constants obtained using Rice-Ramsperger-Kassel-Marcus theory. (C) 2000 Elsevier Science B.V.