Experimental magnetic sublevel scattering-angle-integrated cross sections following ionization-excitation of He(1s 2) 1 S to He + (2p) 2 P o 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, σ 0 and σ 1 , for M L = 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

We report the first experimental results on the state selective cross-section ratio a + */a* of helium for electron and proton impact. Our results show consistently higher yields for electrons than for protons at higher velocities. A comparison is made between the cross-section ratios

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The authors have determined absolute cross sections for ionization-excitation of He by energetic electron and proton projectiles. Using a semi-empirical analytic formula the authors have been able to decompose their He+ (np) cross section data in leading order terms which are proportional to Zpn for n = 2, 3 and 4. In particular the authors have found a strong Zp3 dependence which appears to represent quantum interference effects. The set of amplitude coefficients obtained here is universal for both their electron and proton cross section results from He+ (np) states with principal quantum numbers n = 2 to 5.