Collisional Excitation of Small Molecular Ions

Abstract

We have determined velocity vector distributions for NO⁺ and O₂⁺ scattered from helium. As expected, the small angle scattering is elastic, but at angles greater than 60°, inelasticity which increases with the scattering angle is apparent. For angles greater than 100°, this inelasticity represents vibrational excitation of the molecule–ion. For initial relative kinetic energies between 4.3 and 25 eV and 180° scattering, the variation of the inelasticity is consistent with a new, corrected version of the classical theory of vibrational excitation. Three methods of calculating the angular variation of the inelasticity are presented and found to be consistent with the experimental data.