Penning and associative ionization of argon atoms by excited metastable neon

The associative-to-Penning ionization cross section ratio is simulated with a classical model for the Ne*(P-3(2,0))-Ar collision. We used the semi-classical optical potential curve of Gregor and Siska together with calculated ab initio Ne-Ar+ potential curves to describe the entry and exit channels, respectively. This model which had already been adjusted to fit the total cross section failed to reproduce both the experimental associative ionization cross section and the associative-to-Penning ionization cross section ratio. The contrasting results obtained between theory and experimental data are understood to be the result of an unsuitable real part of the potential for the entrance channel. We did not attempt to modify the average semi-classical potential to fit the experimental data, and it is concluded that an accurate ab initio complex potential is needed for a quantitative analysis of all the observable quantities.