Helium spin-orbit relaxation

Spin-orbit relaxation of Rb(52P) appears to be abnormally slow in all the inert gases except helium (cross-section 10 17 cm2). In fact, according to Pitre et a/.123, the relaxation rate in Kr and Xe is slower than for the equivalent transitions of atomic Cs, which correspond to a three-fold larger change in internal energy. Pitre et al. discuss complications in the rubidium experiments, including the formation of van der Waals complexes with the inert gases, in order to account for the apparently abnormal relaxation rates. Efficient removal of Rb(5 2P) by radiationless processes could upset the derived rate coefficients. The results were discussed in relation to Zener s semi-classical equivalent of equation (14). 

Here Xj is the hydrogenic K-shell electron orbital of the helium ion. Its effective potential is -2e lr 2- An electron, with spin opposite to m, leaving the ion behind with one electron in the ground state Xj sees a potential -2c /r,2 + xy l n Xj)f t.t., a correctly screened potential. Of course this choice does nothing about the ground state wave function of the atom which will still be inaccurate, in this model, as we have used the relaxed orbits of the ion, not the self consistent orbits of the atom, to form the potential. But the main point is that there is no unique choice that can be made. 

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