Kinetics of Cations with C 2 Hydrofluorocarbon Radicals.

Reactions of the cations Ar+ , O2 + , CO2 + , and CF3 + with the C2 radicals C2 H5 , H2 C2 F3 , C2 F3 , and C2 F5 were investigated using the variable electron and neutral density attachment mass spectrometry technique in a flowing afterglow-Langmuir probe apparatus at room temperature. Rate coefficients for observed product channels for these 16 reactions are reported as well as rate coefficients and product branching fractions for the 16 reactions of the same cations with each of the stable neutrals used as radical precursors (the species RI, where R is the radical studied). Reactions with the stable neutrals proceed by charge transfer at or near the collisional rate coefficient where energetically allowed; where charge transfer is endothermic, bond-breaking/bond-making chemistry occurs. While also efficient, reactions with the radicals are more likely to occur at a smaller fraction of the collisional rate coefficient, and bond-breaking/bond-making chemistry occurs even in some cases where charge transfer is exothermic. It is noted that unlike radical reactions with neutral species, which occur with rate coefficients that are generally elevated compared to those of stable species, ion-radical reactivity is generally decreased relative to that of reactions with stable species. In particular, long-range charge transfer appears more likely to be frustrated in the ion-radical systems.