Ionization–excitation magnetic sublevel cross sections for Heþ (2p)P states following fast electron and proton impact

The first experimental magnetic substate scattering-angle-integrated cross sections following ionization–excitation of He(1s) S to Heþ(2p) P in the e þHe collision system 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, r0 and r1, for ML 1⁄4 0, 1 have been studied over a wide range of electron velocities (2–8.5 a.u.). These results are compared with previous cross sections for equi-velocity proton impact. In addition, our experimental data are compared with earlier theoretical predictions, our recent second-Born calculations fully including off-energy shell terms, and new R-matrix results. We have extended our polarization measurements for Hþ þHe collisions and found excellent agreement between theory and experiment at nearly all impact energies. However, the present second-Born and Rmatrix results deviate slightly from the experimental electron data. 2003 Elsevier Science B.V. All rights reserved. PACS: 34.50.Fa; 34.80.Dp