Ionization – excitation of helium to He + ( 2 p ) magnetic sublevels following electron , proton , and molecular hydrogen ( H + 2 and H + 3 ) impact

Experimental magnetic sublevel scattering-angle-integrated cross sections following ionization–excitation of He(1s2)1S to He+(2p)2Po in e− + He and H+ m +He (m = 1–3) collision systems have been determined using a combination of total cross sections and polarization fraction measurements in the extreme ultraviolet range. The derived magnetic sublevel cross sections, σ0 and σ1, for ML = 0 ± 1 have been studied over a wide range of velocities (2–8.5 au) for electron impact on helium. These results are compared with previous experimental proton cross sections (2–6 au) as well as new measured data for hydrogen molecular impact (1.4–4.0 au) for equi-velocity. In addition, our electron and proton measurements are compared with earlier theoretical predictions, our recent second-Born calculations fully including off-shell energy terms, and present predictions from a hybrid first-order and second-order distorted-wave plus R-matrix (close-coupling) model (DWB1 + RMPS and DWB2 + RMPS). Finally, we have extended our polarization measurements for H+ + He collisions and found excellent agreement between theory and experiment at nearly all impact energies. However, the present second-Born and DWB1 + RMPS results deviate slightly from the experimental electron data while the DWB2 + RMPS calculations tend toward the experimental data of Forand et al (1985 J. Phys. B: At. Mol. Phys. 18 1409).