Electron translation factors in orienting charge transfer collisions

The role of the electron translational factors (ETF) in the semiclassical theory of charge transfer is addressed with respect to orientation effects and possible propensity rules in s-p and p-p capture processes. It is shown that orientation effects can be understood in the light of the intuitive classical 'rolling ball' and 'velocity matching' arguments and analysed using the Larsen-Taulbjerg first-order approximation to the ETF. Emphasis is placed on investigating resonant p-p transfer which is a crucial test case for the effects of ETF on orientation dependences. The predictions are exemplified by four-state close-coupling calculations for Na(3p m )+Na + to Na + +Na(3p' m ) resonant transfer taking full account of ETF. Some problems involved in comparing experimental data at small scattering angles with theoretical predictions are discussed.