Role of ionization-excitation processes in the cross section for direct ionization of heavy atomic ions by electron impact

Abstract

The contribution to the ionization cross section of ionization-excitation processes by electron impact is usually negligibly small for low-and medium-Z elements. We demonstrate here, however, that for heavy atomic ions with the outermost shell being nd (n = 4,5) the ionization-excitation processes play an evident role in the ionization cross section. For the 4s 2 4p 6 4d 10 ground level of Gd 18+ , the ionization-excitation cross section due to the excitation of levels in the 4s 2 4p 6 4d 8 4f configuration is comparable to the direct 4p and 4s ionization cross sections of (4s 2 4p 5 4d 10 ) 1/2 and (4s4p 6 4d 10 ) 1/2 . The total ionization cross section will be underestimated by 15% without including the contribution from ionization-excitation processes. This is a general conclusion for heavy atomic ions, which is verified by taking Pd-like ions of Sn 4+ , Ba 10+ , Nd 14+ , Tb 19+ , Yb 24+ , and W 28+ as examples. The role of ionization-excitation processes can be understood from the overlapping of the wave functions between the 4d and 4f orbitals.

A practical theoretical formalism for atomic multielectron processes: direct multiple ionization by a single auger decay or by impact of a single electron or photon

“…The required quantities including the single Auger decay rate, electron-and photonimpact single ionization cross section are obtained using the Flexible Atomic Code developed by Gu 48 and the R-matrix method [49][50][51][52] . The theory on these single electron processes can be found elsewhere [45][46][47][50][51][52][53][54][55] and therefore the details are not given here. To obtain as accurate results as possible, electron correlations should be adequately considered in each step 56,57 .…”

Single and double K-shell resonant photoionization and Auger decay of 1s → 2p excited states of O+–O4+

“…| E, E 0 − E, Ψ 2+ f |E 0 , Ψ + m | means the overlap integral between the wave functions in the potential field of the initial state and that in the final state with two Auger electrons being ejected. The detailed theoretical methods to calculate single Auger decay rate and electron impact single ionization cross section can be found in references (Gu 2008;Zeng et al 2014;Liu et al 2014bLiu et al , 2015 with the data being obtained by using the Flexible Atomic Code developed by Gu (2008).…”