Excitation cross sections of (1snp) [sup 1]P[sup o] (n=2–5) levels of helium by fast electron, proton, and molecular hydrogen (H[sub 2][sup +] and H[sub 3][sup +]) impact

Abstract

Experimental cross sections in the extreme ultraviolet (EUV) wavelength range for the excitation of helium following electron and H+, H2+, and H3+ ion impact are presented for HeI (1snp) 1Po states with n=2–5. These measurements extend over a large velocity range from 3.8–8.5 a.u. for electrons, 1.4–7.5 a.u. for protons, and 1.4–4.0 a.u. for H2+ and H3+ ions, and they represent the most complete data set obtained so far in the EUV. Furthermore, the convergent close coupling (CCC) and R-matrix with pseudo-states (RMPS) methods have been used here to predict excitation cross sections for the HeI (1snp) 1Po states following electron impact and the atomic-orbitals close coupling expansion (AOCC) for proton impact. In particular, our theoretical results are presented and compared with our EUV experimental cross sections for equal projectile velocities together with previous experimental results including cross sections derived from scaling procedures.