An energetic (e, 2e) reaction away from the Bethe ridge: recoil versus binary

Abstract

We analyse the recoil-to-binary (RB) peak intensity ratio in an energetic (e,2e) reaction performed on the valence ns sub-shell of noble gas atoms away from the Bethe ridge condition. A qualitative change in the RB ratio dependence on the ejected electron energy from He to Ar can be explained by the variation of reflectivity of the short-range Hartree-Fock potential. The reflectivity increases profoundly from lighter (He) to heavier (Ne and Ar) noble gas atoms because of modification of the scattering phases due to occupation of the target p orbitals (Levinson-Seaton theorem). This effect is further modified due to strong inter-shell correlations in Ar. These theoretical predictions are confirmed experimentally.

Predominance of the second-order, two-step mechanism in the electron impact double ionization of helium at intermediate impact energy

“…σ /dE a dΩ a dΩ b , for single ionization of the He 1s orbital was measured at the energies E a and E b of the current DI experiments on He and H 2 , immediately before and after each individual (e,3-1e) run. The so-obtained He TDCS-distributions are in excellent agreement both with the experimental values as well as with the calculated convergent close coupling (CCC) results published in[46][47][48]. The CCC model is commonly known to produce very accurate TDCS results for electron impact single ionization of He when the residual ion is left in its ground state.…”

Electron impact double ionization of neon, argon and molecular nitrogen: role of the two-step mechanism

“…It is well established (see e.g. [21]) that, in the incident and ejected energy ranges considered here, the recoil-to-binary (R/B) maximum intensity ratio for the (e, 2e) SI case is generally, although not systematically, smaller than unity and is rapidly decreasing with increasing ejected electron energy. In contrast, we observe here for the case of DI a backward-to-forward (B/F) maximum intensity ratio which is more or less constant versus E b .…”

Energy dependence of the (e,2e) recoil peak to binary peak ratio across He (2p2)1deHarak1, Bartschat2, Martin3 2014Phys. Rev. A3010View full textAdd to dashboardCite

“…Finally, we note that whereas for the case of Ne the anomalously large recoil peak was ascribed to the phase shifts of all partial waves in a Hartree-Fock potential [3,4], for He autoionization the large recoil peaks can be ascribed to an enhanced amplitude for a single partial wave for each resonance, specifically the d wave for (2p 2 ) 1 D and the p wave for (2s2p) 1 P .…”

“…This, however, was not the case for the other targets; for Ne and Ar the recoil peak became larger than the binary peak as the ejected-electron energy was increased, with R RB ≈ 2 at 300 eV. This was explained in terms of the phase shifts * nmartin@uky.edu of the ejected electron partial waves, and an anomalously large recoil peak intensity in Ne 2s 2 was reproduced satisfactorily by partial-wave reflection from a short-range Hartree-Fock potential [4].…”

“…It can also serve as a benchmark for testing state-of-the-art theoretical approaches. Thus experimental and theoretical studies of He, Ne, and Ar [3,4], carried out for a fixed scattering angle θ sc = 6 • and scatteredelectron energy of 500 eV, found recoil to binary ratios (R RB ) that were pronounced functions of ejected-electron energy. For He, the recoil peak was generally much smaller than the binary peak, and R RB was <0.2 for ejected-electron energies >20 eV.…”