We describe a unique indicator for the effect of second-Born-approximation terms in the secondary-electron spectra of continuum-electron capture by positive ions. Specifically, a discontinuity in the function/(t/^ ,t;^ , ^g), where d^a^ if (Ve .Vp , 6^)/Iv^-VplUE^aa^ , indicates second-Born-approximation contributions. Three different experiments are analyzed with respect to this indicator. In all cases we find strong evidence for the discontinuity and hence the presence of second-Born-approximation terms.

We present high-resolution electron spectra for electrons ejected in the forward direction by protons and neutral hydrogen in collisions with He gas. The spectra show the expected electron transfer to the continuum peak, but also show a 0° ridge extending to the lowest electron energies measured. We propose that this new secondary-electron component represents electrons which propagate on the saddle of the potential surface produced by the two positive ions H"*" and He"^ in the intermediate collision complex.

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The Heresonances at 57.1 and 58,2 eV in the electron scattering from He were studied as a function of angle in three inelastic channels corresponding to excitation of the (U2s) z S, (IslsYS, and (ls2p) 1 P states of He. The line shapes of the resonances are found to vary with angle. The application of the Fano-Cooper formula, developed for the case of photon absorption, to resonances in inelastic electron scattering is discussed, along with a simple procedure for determining the line profile indices. The angular dependence of the l S, 3 5, and l P excitations at 56.5 eV was also measured out to about 60°. Q UJ N ZJ < 2