Selection rules for transitions to two-electron continuum states

Abstract

A continuum state of two electrons with momenta k1 and k2 can be represented as a linear combination of two-electron states with quantum numbers L, M, S and pi . Conditions are derived for which a given LMS pi state gives a vanishing contribution to the population of a state of given k1 and k2 in an arbitrary process leading to a two-electron continuum state.

Double photoionization of excited lithium and beryllium

“…The He cross sections are generally larger than the corresponding Be cross sections, but the relative contributions of the vari-ous symmetry components to the total are similar. Several selection rules are evident in the results, namely, that the 3 S and 1 P e contributions vanish at equal energy sharing [14]. Curiously, the P e component, which only contributes to DPI with perpendicular polarization, is vanishingly small at all energy sharings in the case of the 1 P 0 targets, but is the dominant component in the case of the 1 P 0 targets.…”

“…It is evident that the angular distributions are very sensitive to the orientation of the polarization. In all cases, we observe that the "B1" selectrion rule [14] is satisfied, which states that both electrons can't go out perpendicular to the polarization direction for final state M not equal to zero. This is evident for the Θ 1 = 0 • panels in Figs.…”

Laser-assisted XUV double ionization of helium: Energy-sharing dependence of joint angular distributions

“…3(a)]. In compliance with known selection rules for DI at equal energy sharing [1,13], side-by-side and back-to-back emission are prohibited. This graph also shows good agreement of our calculation with the theoretical results of Huetz et al [6,10].…”

“…Back-to-back emission now occurs, while side-by-side emission remains prohibited as for the case of equal energy sharing [1,13]. [28].…”

“…Soon afterwards, Briggs and coworkers derived selection rules for helium DI, emphasizing their relevance for the understanding of photoelectron angular distributions [1,[11][12][13][14]. The convergent close-coupling (CCC) calculations by Keifets and Bray [6], TDCSs calculated by Huetz et al [6,10], as well as TDCSs obtained from timedependent close-coupling (TDCC) simulations by Palacios et al [15] were found to be in good agreement with the angular distributions in the absolute TDCSs for the DI of helium by 99 eV XUV photons measured by Bräuning et al [6].…”