Electronic excitation of H₂ in slow collisions with molecular ions

Abstract

Excitation of molecular hydrogen has been studied in 1.8-keV collisions with molecular projectile ions H₂⁺, N₂⁺, CO⁺, O₂⁺, and CO₂⁺ by means of energy-loss spectrometry using a high-resolution ion translational-energy spectrometer. Excitation of the target H₂ is observed only in the case of collisions with H₂⁺. Oscillator strengths for electronic transitions to various electronic states are determined by simulating the measured energy-loss spectra with calculations using calculated Franck-Condon overlap integrals. Excitation of the projectile ions is observed in the case of collisions with N₂⁺ and CO+ projectiles. Neither projectile excitation nor target excitation is observed when experiments are carried out with O₂⁺ and CO₂⁺ projectiles. The results obtained in the present study are interpreted as a manifestation of wave-function-overlap effects involving the highest occupied molecular orbitals of the target and projectile ions.