Cross sections for symmetric charge transfer and proton transfer reactions of internal energy selected NH3+ (v)

Abstract

Absolute total cross sections for electron and proton transfer reactions of NH3 selected in vibrational levels from v = 0 to 10 have been measured by photoion–photoelectron coincidence. The proton transfer reactions were determined at relative translational energies between 0.1 and 1 eV, while the electron transfer reactions were measured between 1 and 100 eV and at 3000 eV. Although the Franck–Condon factors between v = 0 and v = 5 of the NH3 (v = 0)→NH3+ (v) transition change by a factor of 35, the cross sections for charge transfer vary only by a factor of two. By comparing the measured cross sections with the Langevin collision cross sections, we show that the internal energy plays a role only for impact parameters larger than the Langevin orbiting impact parameter. A model which divides the charge transfer reaction into two types, one involving intimate collisions, the other large impact parameter collisions, is introduced. The model is used to derive the charge transfer probability as a function of impact parameter for various combinations of NH3+ vibrational and relative kinetic energies.