Quantum-Mechanical and Experimental Study of the Excitation of the2P1State of He by Electron Impact at 29-40 eV

Proposed standard inelastic differential electron scattering cross sections; Excitation of the 21 P level in He

“…At larger scattering angles, the signal levels are low and large statistical errors are encountered or, because of long data-collection times, instrumental drifts can occur. Truhlar et al [12] measured relative DCS (20 °) at 29.6 and 40.1 eV impact energies as a function of scattering angle. We, therefore, put the emphasis on the DCS (20 °) data, but also discuss the situation at other angles.…”

“…Phase shift analysis of relative elastic DCS's [3][4][5], normalization to the well established He elastic DCS [6][7][8] and normalization to the known total electron scattering cross section [5, have all been used by various authors to obtain absolute elastic DCS's. Normalization to optical excitation functions has also been used [12], but optical excitation function measurements have many of the same problems as direct absolute electron scattering cross section measurements and in addition have to be corrected for cascade effects to transform them into electron impact excitation cross sections. Although normalization to optical f-values or to theory has been used at intermediate impact energies [t0, 11], these approaches are not reliable at intermediate and low energies.…”

“…Summary of the He 21P DCS measurements Vriens et al 1,27] Normalization to optical f-value c Suzuki and Takayanagi [31] -Normalization to elastic DCS's of Bromberg [32] or to 5 ° 21P DCS's of Chamberlain et al Cartwright et al [15] -Normalization to He elastic DCS g Chutjian and Srivastava [34] -Normalization to He elastic DCS h Hall et al 1,8] -Normalization to He elastic DCS J Truhlar et al[12] Normalization to 21P integral cross section obtained from optical excitation function k Brunger et al[36] -Normalization to 2 ~P integral cross section recommended by de Heer and Jansen[37] …”

Electron impact differential and integral cross sections for excitation of the n = 2 states of helium at 29.2 eV, 39.2 eV and 48.2 eV

“…In pioneering work, Trajmar and coworkers [14]- [16] measured differential cross sections for these states between 26 eV and 55 eV up to a 700 scattering angle and placed them on an absolute scale by normalization to the optically measured 2 1P integral cross sections of Jobe and St. John [8]. Very recently this group has performed new and more accurate measurements at 29 eV and 40 eV [17]- [18] up to 1400 but this time normalized their results to the recent optical 2 1 P integral cross sections of Donaldson et al [11]. Crooks and coworkers [19], [20] have also very recently determined differential cross sections in the 50 eV energy region.…”

Structures in Electron-Impact Excitation Cross Sections of He from 30 to 70 eV

“…1 " 3 These features have not been predicted by previous calculations of electron-helium scattering employing various forms of semiempirical optical and polarization potentials, 4 nor by variational calculations, 5 ' 6 nor by the close-coupling approximation invoking the participation of doubly excitated states of He. 7 Because recent work has shown that the close-coupling approximation does correctly describe the general shape of the differential cross section for electrons on alkali atoms, 8 and to some degree the 2 l P electron excitation of He, 9 we have investigated the intermediate energy region with the close-coupling formalism which has previously been successfully used to predict and interpret structures in electron-impact helium excitation functions in the vicinity of the n = 2 threshold. 10 Among other results, we find that the essential experimental findings 1 " 3 can be adequately reproduced even with calculations involving only the simplest possible (three S states) eigenfunction expansion.…”