Impact parameter dependence of light-ion electronic energy loss

We have calculated the dependence of the mean electronic energy loss of light ions on impact parameter by use of the harmonic-oscillator model of atomic stopping. Results are reported for protons incident on atomic hydrogen, helium, neon, and argon at velocities υ≥υ0. Considerable care has been taken in selecting proper sets of dipole oscillator strengths to characterize the ensemble of harmonic oscillators. The energy transfer to an individual oscillator is known from our previous work to the three leading orders in the Born series. Mainly first-order results have been analysed. We find a quasi-Gaussian behavior at small impact leading orders in the Born series. Mainly first-order results have been analysed. We find a quasi-Gaussian behavior at small impact parameters and a nearly exponential tail at larger impact parameters. The latter approaches Bloch's dipole limit which is asymptotically exact. A single-oscillator model is included in the comparison and turns out to be inadequate in all cases except for high-speed protons incident on hydrogen. Part of our results can be compared with those of Kabachnik et al. The overall agreement is reasonable, but discrepancies of up to a factor of 2 have been found. For atomic hydrogen, these inaccuracies are asserted to originate in their numerical procedure. (orig.)