Potential energy curves for the collisional excitation of the(HeNe)+system

The adiabatic spectrum of potential energy curves, corresponding to the ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\Pi$ states of the molecular complex, have been calculated using an ab initio configuration-interaction method. Curve-crossing phenomena are found in all the curves with the exception of the lowest ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ state, corresponding to the ${\mathrm{Ne}}^{+}\left({}_{}{}^2{}_{}{}^{}P\right)+\mathrm{He}\left({}_{}{}^1{}_{}{}^{}S\right)$ asymptotic level. An approximate threshold of 22 eV is predicted for the neon ${}_{}{}^1{}_{}{}^{}S$ to ${}_{}{}^1{}_{}{}^{}P$ excitation, which is in good agreement with available experimental predictions. The charge-exchange excitation of Ne in the ${\mathrm{Ne}}^{+}$ + He collision occurs at about 29 eV in the ${}_{}{}^2{}_{}{}^{}\Pi$ state for an internuclear separation of $1.5a_0$. Three additional crossings for the ${}_{}{}^2{}_{}{}^{}\Pi$ spectrum are also found at lower energy and larger separation. The cross section for the first ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$ crossing is calculated as a function of collision energy using the Landau-Zener-Stueckelberg method, and including the phase-interference effect. Phase-interference ("Stueckelberg") oscillations are found in the cross section and are in qualitative agreement with oscillations found in the experimental cross sections.