Collision-induced intramultiplet mixing for Ne**{(2p)5(3p)} + Ne: principles and practice of symmetry effects

We present an extension of the model-potential method of Ne**{(2p)5(3p)}-Ne collisions. The role of the electronic inversion symmetry in the core–valence-electron separation for stationary nuclei is examined. This leads to approximate electronic eigenfunctions and corresponding adiabatic potentials. In this, an essential element is the R-dependent mixing of gerade and ungerade core potentials, associated with the R-dependent uncertainty of the valence electron being located at the Ne+ ion or the Ne atom. Subsequently, nuclear dynamics is included in the approximate wave function and the role of the identity of the nuclei is considered. With the aim of testing our extended approximate treatment, we also present experimental 20Ne**-Ne, and 22Ne**-Ne total polarized cross sections Ql¿k¿Mk¿ for the {(2p)5(3p)}k (or {a}k¿{a}l) transition, with Mk the magnetic quantum number of the electronic angular momentum J of the initial {a}k state with respect to the asymptotic relative velocity. Considerable polarization effects have been observed, as well as some interesting differences with earlier Ne**-He data, but no significant differences between the results for 20Ne and 22Ne. Preliminary quantum-mechanical coupled-channel calculations for the Ne**-Ne problem, using valence-electron potentials from Hennecart and Masnou-Seeuws and core potentials from Cohen and Schneider as input, allow us to test theory against experiment, a procedure proven successful for the Ne**-He system. We distinguish between the two limiting cases of complete and zero mixing of the gerade and ungerade core potentials. Complete mixing gives much better agreement. For example, the experimental polarization effect Q6¿5¿0¿/Q6¿5¿1¿=2.1 should be compared to the predictions 1.9 and 0.3 for complete and zero mixing, respectively. In general, the measure of agreement obtained for complete mixing indicates the relative lack of importance of symmetry effects for the thermal energies investigated.