Spin exchange in the excitation of spin-polarized Na atoms by Ne + -ion impact

The 3s-3p excitation of spin-polarized Na atoms by Ne/sup +/ ions has been studied for impact energies E/sub lab/ = 200 eV to 6 keV, i.e., in the adiabatic regime. The total excitation cross section and the three Stokes polarization parameters of the fluorescence light have been measured. The linear polarization of the light shows a preferential excitation of the chemically bondm/sub l/chemically bond = 1 magnetic substates. The circular polarization probes the spin orientation of the excited 3p state. At the highest impact energies investigated the experimental data are compatible with conservation of spin orientation during the collision. With decreasing impact energy, the spin polarization of the final 3p state becomes smaller than the spin polarization of the initial 3s state. This apparent spin depolarization is attributed to the exchange interaction between the Na valence electron and the unfilled Ne/sup +/ 2p/sup 5/ core in the quasimolecule formed during the collision.