Fragmentation and Structure of C2H3S(1+) Ions

Article abstract of DOI:10.1021/ja00185a012

Daughter spectra for C2H3S(1+) ions, generated from a variety of precursor molecules and activated by different means, are insensitive to the nature of the precursors, but spectra recorded by different methods of activation show unexpectedly large differences.The methyl cation, a fragment characteristic of the thioacylium structure, is the dominant product of collisions at low energy with a gaseous or solid target but is virtually absent for zero scattering angle gas-phase collisions in the kiloelectronvolt range.As the scattering angle is increased, this low-energyfragment increases in abundance, and it is suggested that this is the result of an increased degree of direct vibrational as opposed to electronic excitation.It is shown that (i) the C2H3S(1+) ions sampled by collision-activated dissociation and by surface-induced dissociation have the thioacylium structure, (ii) internal energy differences associated with their formation are not reflected in spectral changes in kiloelectronvolt collision experiments although they do affect the low-energy spectra, (iii) zero-angle, high-energy collisions probably involve fragmentation via excited electronic states, and for this reason they result in different products to those that occur upon low-energy collisions with gaseous or solid targets, and (iv) while activation by collision with a solid surface in the energy range below 100 eV causes very considerable internal excitation, only vibrational and not electronic excitation is involved.Isomerization between the several nascent C2H3S(1+) structures generated from different precursors occurs prior to activation and is favored by the unusually high activation energy required for dissociation.Whenthe highly endothermic charge stripping process is used, it is possible to sample some C2H3S(1+) ions of such low internal energy that they have not completely isomerized.