Zero-degree target electron spectroscopy: autoionizing resonances of helium excited by fast H⁺, He⁺and He²⁺impact

Abstract

Two-electron excitation and decay of the autoionizing (2p 2 ) 1 D and (2s2p) 1 P states of helium in collisions with fast protons and helium ions have been studied using zero-degree target electron spectroscopy. The energy resolution of electron emission spectra is 80 meV. Experimental spectra were processed using a parametrization with allowance for the Coulomb interaction in the final state (CIFS) between the ejected electron, the scattered ion and the recoil helium ion. The Shore formula was applied as well. Calculations have been carried out with inclusion of CIFS in both direct and resonant ionization amplitudes and within an expansion of a two-electron excitation amplitude in powers of projectile-target interaction up to the second order. Influence of the three-body Coulomb interaction and effects of the charge and mass of the projectiles are studied.

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

“…There is at present a considerable interest in few-electron processes induced by intermediate to high-energy charged particle impact on atomic and molecular targets (McGuire 1997, Bruch et al 1993 such as double ionization, double excitation (Bruch et al 2002), and ionization-excitation. These many-body aspects of atomic collision processes are associated with electron-electron correlations and other few-body dynamical phenomena that supersede independent-particle models (Niehaus 1986).…”

A convenient formalism for Auger and autoionization of overlapping resonances

“…Godunov et al [7] presented a general comprehensive formula for isolated resonances. The isolated resonance treatment has been successfully adapted for many different systems: for (e, 2e) in helium [8][9][10][11][12][13][14][15]; helium ionization by proton impact [7,16], by proton and antiproton impact [17] and by H + , He + and He 2+ impact [18]. The isolated resonance treatment was also applied to heavy atoms such as (e, 2e) in cadmium [19][20][21][22].…”