N2+ (A 2Piu from X 2Sigmag+) excitation in the charge-exchange collision with caesium: two-electron effects at keV energies

Abstract

Charge-exchange collisions of 5 keV N2+ on Cs are examined using translational spectroscopy to identify the internal energy states of the fast neutralized products. Optical pumping of the reactant, N2+(A from X) or Cs(2P from 2S), is used to change selectively the electronic configurations and the reaction energy defect, while monitoring the resulting changes in the product state distribution. The N2+/Cs charge exchange yields N2 Rydberg states. A simple model of their formation would involve the transfer of the single outer electron in Cs into a Rydberg orbit built on the N2+ core. However, the present studies identify a surprising and highly efficient reaction mechanism in which the electronic configuration of the N2+ reactant is also changed during the electron transfer. This facile two-electron process, which occurs for both near-resonant and non-resonant reaction channels acid has not been observed in other molecular charge-transfer reactions, is believed to be related to the very small energy separation between the ground and first excited electronic states of N2+.