Velocity dependence of Rydberg n to n' charge transfer cross sections

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Abstract
Measurements of the distribution of final n' states that are populated in charge transfer collisions of Ar+ and Na+ ions with Na in the 25s state are reported. Collision energies range from 580 to 2000 eV corresponding to projectile speeds v1 from 0.572 to 1.400 times the RMS electronic orbital speed vi in the initial state (v=v1/vi). The data are presented on a common relative scale of cross sections to indicate velocity or energy dependence. The cross section summed over all final states n' is of the form sigma 12/=A-B in v and agrees qualitatively with the velocity dependences of a Brinkman-Kramers (BK) calculation and of scaled experimental data for p+H(1s) to H (all states)+p. The data disagree with classical trajectory Monte-Carlo calculations for v<1. Relative cross sections for n to n' are also presented for n'=20 and 40. The peak positions and widths of the final-state distributions are compared with the predictions of the BK approximation. There is satisfactory agreement for low and intermediate final n', but the measured distributions show less than the predicted population of high final states.