Oscillatory Structure in Total-Charge-Transfer Cross Sections

Oscillatory structure has been observed in total symmetric and asymmetric charge-transfer cross-section measurements involving the alkali-metal atoms. Cross sections with oscillations similar to experimental results had been obtained from impact-parameter calculations using a two-state approximation with an interaction potential difference containing a maximum. This paper describes a physical model of charge transfer relating to the oscillatory electron capture probability. The Li⁺ + Li calculations of Peek et al. are examined and used as an example to relate capture-probability oscillations to those in total cross section. Computed capture probabilities having anomalous oscillations are shown as a function of impact parameter at several velocities. The capture-probability maxima are shown as contours on a plot of impact parameter versus inverse impact velocity. This plot illustrates capture-probability oscillations having a nearly stationary phase over a range of impact parameters, which results in oscillations in the total cross section. Oscillation damping and phase-constant effects are briefly examined to relate experimental results with theory. Near-resonant asymmetric oscillations are also discussed.