Charge transfer and collision-induced dissociation reactions of CO++ with the rare gases at Elab=49 eV

Abstract

Multiple product channels are observed for the reaction of 13CO++ with each of the rare gases (Rg) at Elab=49±1 eV. A beam of 13CO++ is produced by electron impact ionization and is mass selected using a quadrupole mass spectrometer. The ion beam is focused into a collision region and the reaction products are monitored using time-of-flight mass spectrometry. Relative yields for the production of 13C+, O+, and 13CO+ are measured directly. Absolute charge transfer reaction cross sections for collisions of 13CO++ with He, Ne, Ar, and Kr are estimated by comparing the Rg+ production with that for the charge transfer reactions of doubly charged rare gas ions with neutral rare gas atoms. The cross sections are found to range from 0.9−0.9+1.5 Å2 for collisions of 13CO++ with He to 37.5±19.6 Å2 for collisions with Kr. The reaction of 13CO++ with He proceeds almost exclusively into the collision-induced dissociation channel. The branching fraction for collision-induced dissociation is smaller for reactions with Ne and almost disappears for Ar, Kr, and Xe. As the relative importance of the collision-induced dissociation process decreases, branching into the charge transfer channel increases. The charge transfer reactions of 13CO++ with Ar, Kr, and Xe are shown to populate excited, dissociative electronic states of 13CO+ selectively. These effects are modeled successfully using Landau–Zener theory in conjunction with reaction window theory.