Reactivity of Halogenoethylene Ions using Photoionization and Collisional Activation.

Unimolecular reactivity of ionized difluoroethylene and vinylbromide have been investigated using photoionization mass spectrometry and tandem mass spectrometry. Kinetic energy release distributions corresponding to HF- and F- losses from 1,1-C2H2F2+ and to Br-loss from C2H3Br+ have been determined. At low internal energy the loss of HF from C2H2F2+ leads to the fluoroacetylene cation with a large kinetic energy release (0.4-2.5 eV) while at higher energy a new channel is opened, leading to C=CHF+ (fluorovinylidene) with a much smaller kinetic energy release (0.0-0.2 eV). For the F-loss from C2H2F2+ and the Br-loss from C2H3Br+ bimodal distributions have been observed. The possible role of excited states in these dissociations is discussed.