Superelastic Collisions of Vibrationally ExcitedH2+with Atoms and Molecules

We report the direct experimental observation of superelastic collisions of vibrationally excited $\mathrm{H}_2^{}{}_{}{}^{+}$ ions with atomic and molecular targets. Energy-change spectra taken with $\mathrm{H}_2^{}{}_{}{}^{+}$ incident on He, Ne, Ar, Kr, and ${\mathrm{H}}_2$ targets show a strong dependence of the cross section on the atomic number of the target. The cross sections for superelastic collisions were observed throughout the kinetic-energy range 100-1500 eV and they appear to be largest in the region 100-500 eV, decreasing slowly at higher energies.