R. Bruch et al., EXCITATION AND IONIZATION IN FAST-ELECTRON AND ION COLLISIONS WITH HELIUM GAS TARGETS, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 79(1-4), 1993, pp. 120-123
Extensive research has been conducted in our laboratory on absolute cr
oss section measurements of extreme ultraviolet (EUV) emission spectra
following e-, H+, H-2+ and H-3+ high energy bombardment of He gas tar
gets. In particular higher order contributions which vary as the cube
of the projectile charge Z(p) have been studied for joint ionization-e
xcitation of He. These terms of odd order in Z(p) may represent comple
x quantum interference effects. Using a semiempirical analytic formula
we have been able to decompose our cross section data in leading orde
r terms which are proportional to Z(p)n for n = 2-4 for electron and p
roton impact. This approach allows us to model the charge-state, veloc
ity- and Rydberg state dependence of ionization-excitation cross secti
ons at velocities v/v0 = 3.5-8 for He+ (np) states.