Excitation of XeI resonance lines inXe+/Xe collisions

Symmetric ion-atom reactions in xenon of the type ${\mathrm{Xe}}^{+}$ + Xe→${\mathrm{Xe}}^{+}$ + Xe* have been found to occur with large cross sections at collision energies below 50 eV (c.m.). The reaction cross section for production of the two lowest Xe resonance levels $6s{\left[\frac{3}{2}\right]}_1^o$ and $6s^{\prime }{\left[\frac{1}{2}\right]}_1^o$ at collision energies of 7-50 eV have been measured by monitoring the 147.0- and 129.6-nm XeI lines. All reactions involving ${\mathrm{Xe}}^{+}\left({}_{}{}^2{}_{}{}^{}P_{\frac{3}{2},\frac{1}{2}}^o{}_{}{}^{}\right)$ impacting ions display kinetic-energy thresholds corresponding to the transfer of more than 11 eV of translational energy into internal energy. Experimental kinetic-energy thresholds exceed the thermochemical energy difference between the reactants and products evaluated under infinite separation conditions. Excitation of the lowest resonance level of Xe, $6s{\left[\frac{3}{2}\right]}_1^o$, is found to depend strongly upon the electronic state ${}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^o{}_{}{}^{}$ or ${}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^o{}_{}{}^{}$, of the reacting xenon ions.