Anomalous Vibrational-State Distribution inN2+(BΣu2+)after Charge Exchange ofHe2+withN2

We measure cross sections for ${{\mathrm{N}}_2}^{+} \left(B{}_{}{}^2{}_{}{}^{}{\Sigma }_{\mathrm{u}}_{}^{+}{}_{}{}^{}\right)$ production in 5-eV ${\mathrm{He}}_2^{+}$-${\mathrm{N}}_2$ and ${\mathrm{He}}^{+}$-${\mathrm{N}}_2$ collisions by observation of emission in the first negative system of ${\mathrm{N}}_2^{+}$. For ${\mathrm{He}}_2^{+}$ the cross section is unusually large (∼10 ${\mathrm{\AA }}^2$) and the vibrational-state distribution shows primarily $v^{\prime }=0\mathrm{} \mathrm{and} 1$, consistent with vertical ionization of ${\mathrm{N}}_2$. ${\mathrm{He}}^{+}$ produces a much wider distribution, as do most other simple ions. Explanations for the large cross section and observed state distributions are proposed.