Ionization–excitation of helium to He (2p) magnetic sublevels following electron, proton, and molecular hydrogen (H₂ and H₃ ) impact

Abstract

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

NonperturbativeB-splineR-matrix-with-pseudostates calculations for electron-impact ionization-excitation of helium to then=3states ofHeZatsarinny1, Bartschat2 2016Phys. Rev. A6110View full textAdd to dashboardCite

“…As discussed in detail for the corresponding He + (2p) case [3], the absolute value of the cross section was the subject of a longstanding debate due to the difficulties associated with the required experimental normalization procedure. For the 2p case, our recent calculations [3] strongly supported the early normalizations suggested by Bloemen et al [17] and Forand et al [18] over a later attempt by Merabet et al [22]. Furthermore, we found that hybrid models as well as fully perturbative calculations underestimated the cross section significantly.…”

Benchmark calculation of total cross sections for ionization–excitation of helium

“…Our BSRMPS results, however, clearly favour the original normalizations [26,27]. While improving the first-order hybrid model for the projectile towards an effectively converged solution of the ejectedelectron-residual-ion part of the problem in the DW-23CC model [25,28] reduces the magnitude of the predicted cross section, higher-order effects apparently increase it again, thereby making the simplest hybrid model (PW-3CC [29]) accidentally looking the best.…”

“…Our results for the absolute value of the total cross section for simultaneous ionization plus excitation of helium to the He + (2p) ionic state are presented in figure 1. After carrying out their measurements, Merabet et al [25] suggested three Absolute cross sections for simultaneous electron-impact ionization and excitation of He (1s 2 ) leaving the residual ion as He + (2p). The present results, obtained in a BSR model with a total of 525 coupled states by either the decomposition approach (thick solid red line) or the integration method (solid circles at 100, 155, and 195 eV), are compared with experimental data by Bloemen et al [26] (only available at 200 eV), Forand et al [27], and Merabet et al [25], and with a few other theoretical predictions, including three hybrid models (PW-3CC [29], DW-6CC [30], DW-23CC [25,28]) and three points at 100, 150 and 200 eV from a TDCC model [31].…”

Anisotropy in excitation-ionization double-differential cross sections

“…A series of results were published in the 1990s and 2000s that provided differential cross sections for EI leading to determination of various alignment parameters, electron-photon correlations, and Stokes parameters [19][20][21][22][23][24][25][26]. These joint experimental and theoretical studies typically examined scattering angle integrated cross sections, total cross sections, or photon polarization or angular distributions.…”