Feshbach projection approach to study plasma effects on doubly excited autoionizing states in helium

Abstract

We have implemented a method based on the Feshbach formalism along with an explicitly correlated configuration interaction method to perform a systematic study on the behavior of resonance parameters (energies and lifetimes) of the autoionizing states of plasma-embedded He 1,3 S e , 1,3 P o , and 1,3 D e , as a function of the screening strength. In particular, we study the evolution of the lowest states in the series located below the He + (N = 2) ionization threshold in the unscreened case. At variance with one-electron atoms (where shape resonance widths vary monotonically with the screening strength) the evolution of the Auger width with respect to screening is found to be different for each series represented by (K,T ) A pseudoquantum numbers until resonances merge into the upper electronic continuum, when crossing the He + (2s) threshold. We conclude from our ab initio calculations that, although resonances pertaining to the same (K,T ) A series share a similar tendency in their widths against the screening strength, general propensity rules for the robustness of lifetimes, based on the isomorphic series in the (K,T ) A classification, cannot be established in plasma-embedded helium.

Low-energy electron elastic scattering and impact ionization with hydrogenlike helium in Debye plasmas

“…(−0.777 810, 4.58 × 10 −3 ), (−0.760 461,2.99 × 10 −4 ), (−0.701 610, 2.38 × 10 −3 ), and (−0.692 805, 1.37 × 10 −3 )) for the 2s 2 1 S e , 2s2p 3 P o , 2p 2 1 D e , and 2s2p 1 P o resonances, respectively. The calculated resonance parameters agree very well with those published by other authors [23,43].…”

“…2 D e hardly change for all the selected screening lengths, which agrees very well with the structure calculations for those resonances in Refs. [15,23] (see Fig. 4 of the resonances in the hyperspherical coordinate representation.…”

“…Figure 4 shows the dynamic variation of resonant positions (data from Refs. [15,23]), together with the energy differences between the energy levels of He + (n = 2) and He + (n = 1) for different screening lengths. Since the lower orbitals 2l(l = s,p) of He + (and other hydrogenlike ions) are tightly bound, from a very naive picture, the orbitals of the two electrons in the present studied resonances (doubly excited states 2l 2l of He) should be close to orbitals 2l of He + with orbital energy E He + (2l) , i.e., the energy of the resonance equals approximately to the orbital energies of the two electrons (E He + (2l ) + E He + (2l ) ) corrected with the electron-electron interaction (V ee ).…”

“…They have also calculated the energies of bound states of helium atom in Debye plasmas by using the Rayleigh-Ritz variational method [19,20]. Doubly excited states of He in Debye plasmas have also been calculated by Chakraborty and Ho [21] employing the complex-coordinate rotation method, Lin et al [22] using the configuration-interaction approach with B-spline basis functions, Ordóñez-Lasso et al [23] using the Feshbach projection approach, and Jiao and Ho [24] employing the variational and complex-scaling methods. In contrast, Zhang et al have studied the collision dynamics of low-energy electron-hydrogen-atom scattering in the screened Coulomb potential (1) by employing the R-matrix method with pseudostates (RMPS) [25][26][27].…”

Nonrelativistic structure calculations of two-electron ions in a strongly coupled plasma environment

“…The present study is focused on atomic systems embedded in plasma environment. In recent years, atoms placed in external plasma environment have received considerable attention from researchers [11][12][13][14][15][16][17][18][19] due to their wide applications in various disciplines of science e.g. astrophysics, condensed matter physics, biology etc.…”