Non-statistical magnetic substate populations following excitation of helium by electron and proton impact

Abstract

The first experimental magnetic substrate scattering angle-integrated cross sections following excitation of He (1s2)1S to He (1snp)1Po (n=2–5) in e−+He and H++He collision systems have been determined using our differential cross sections and polarization fraction data in the extreme ultraviolet (EUV) range. The derived magnetic sublevel integrated cross sections, σ̄0 and σ̄1, for ML=0,±1 have been studied over a wide range of projectile velocities: 1.4 to 8.5 a.u. and 1.4 to 7.5 a.u. for electron and proton impact on helium, respectively. In addition, the electron and proton collision data are compared with theoretical predictions using our improved first Born approximation (IFB), convergent close coupling (CCC) calculations for electron impact, and our recent atomic orbital close coupling (AOCC) calculations for protons. We have found that the electron results match very well the CCC predictions at all energies. However, the experimental proton data slightly deviate from the AOCC approach at intermediate velocities. Such findings are relevant to plasma and astrophysical applications.