EXCITATION AND IONIZATION IN FAST-ELECTRON AND ION COLLISIONS WITH HELIUM GAS TARGETS

Extensive research has been conducted in our laboratory on absolute cross section measurements of extreme ultraviolet (EUV) emission spectra following e-, H+, H-2+ and H-3+ high energy bombardment of He gas targets. In particular higher order contributions which vary as the cube of the projectile charge Z(p) have been studied for joint ionization-excitation of He. These terms of odd order in Z(p) may represent complex quantum interference effects. Using a semiempirical analytic formula we have been able to decompose our cross section data in leading order terms which are proportional to Z(p)n for n = 2-4 for electron and proton impact. This approach allows us to model the charge-state, velocity- and Rydberg state dependence of ionization-excitation cross sections at velocities v/v0 = 3.5-8 for He+ (np) states.