The state dependence of the interaction of metastable rare gas atoms Rg* (ms 3P2, 3P0) (Rg = Ne, Ar, Kr, Xe) with ground state sodium atoms

Using crossed beams of metastable rare gas atoms Rg*(ms 3P2, 3P0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s 2S1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(3P2)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depths De* [meV] decreasing slowly from Rg=Ne to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(3P0)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depths De* [meV] of: 51(I9); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valence s-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratios q2/q0 of the ionization cross sections for Rg*(3P2)+Na and Rg*(3P0)+Na vary strongly with the rare gas from Ne to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4).