Cross sections for the ionization-excitation of helium by fast electrons and H+, H2+and H3+ions: (np)2P0levels, n=2-5

Cross sections for the ionization-excitation of helium following electron and H + , H 2 + and H 3 + ion impact have been measured for He II (np) 2 P 0 states with n=2-5. These measurements were performed for the velocity range from 3.8-8.5 au for electrons, 1.4-7.5 au for protons and 1.4-4.0 au for H 2 + and H 3 + ions. The cross sections have been obtained by measuring the extreme ultraviolet (EUV) emission from the decay of the excited target atoms at 90 degrees to the projectile beam. We have compared our results to the current limited literature for He II (2p) 2 P 0 cross sections with good agreement observed. We have also examined the cross section ratio of ionization-excitation to excitation, sigma + *((np) 2 P 0 )/ sigma *((1snp) 1 P 0 ), for electron and proton impact in comparison with the ratio of double to single ionization, sigma ++ / sigma + , as a limiting value for large n. Finally, cross section results from H n + impact, where n=1-3, are discussed in terms of a semiempirical scaling relation for molecular hydrogen projectiles.