Photoionization study of Xe 5s: ionization cross sections and photoelectron angular distributions

Abstract

We report studies of photoelectron angular distribution and cross-section for photoionization of xenon 5s electrons using the relativistic multiconfiguration Tamm-Dancoff (MCTD) approximation. We find that MCTD provides a significantly improved agreement with experiment, compared to some of the other relativistic many body approximations such as the relativistic random phase approximation and the relativistic random phase approximation with relaxation, over the entire photon energy region bracketing the near-threshold 5s Cooper minimum, from the 5s threshold up to about 70 eV. The MCTD results in the length form are in much better agreement with the experiment than those in the velocity form, suggesting residual correlations that must be of importance.

Photoionization of atomic barium subshells in the4dthreshold region using the relativistic multiconfiguration Tamm-Dancoff approximation

“…Unfortunately, there are only a few studies in which the RMCTD method has been tested. For example, it has been used to account for photoionization of a very few atoms, Mg and Be [13], Cd [30] and Xe [31] and photodetachment of a few negative ions [32,33]. The present study tests the applicability of the RMCTD to a rather highly correlated atom, atomic barium.…”

Angular dependent time delay near correlation induced Cooper minima

“…The corresponding velocity gauge results (not shown) deviate from the experiment (Fahlman et al 1983) even stronger than RRPA with the parameter for Xe reaching nearly -1 near the CM. The strong e↵ect of the ground state correlation on the ns photoionization near the Cooper minimum can be understood from the multi-configuration expansion presented in (Aarthi et al 2014) for Xe. This expansion contains excitations in the following generic form: 5p 2 ⌫ 1/2 5p 4 µ 3/2 5d ⌫ 3/2 5d µ 5/2 , ⌫, µ = 0, 2, 4 As is seen from Equation (9), the 5d 3/2 bound state can be ionized to both the Ep 1/2 and Ep 3/2 continua whereas the 5d 5/2 state can only couple to the Ep 3/2 one.…”

“…However, the nature of this deficiency A c c e p t e d M a n u s c r i p t has not been addressed and explained until recently. Aarthi et al (2014) suggested that this deficiency can be remedied by inclusion of (i) the ground state correlation and (ii) certain two-electron excitation and ionization channels. Indeed, the MCTD calculation for Xe (Aarthi et al 2014) is much closer to the experimental data (Fahlman et al 1983) than the RRPA, both for the cross-section and the parameter (right panels of Figure 1 and figure 2, respectively).…”

“…Aarthi et al (2014) suggested that this deficiency can be remedied by inclusion of (i) the ground state correlation and (ii) certain two-electron excitation and ionization channels. Indeed, the MCTD calculation for Xe (Aarthi et al 2014) is much closer to the experimental data (Fahlman et al 1983) than the RRPA, both for the cross-section and the parameter (right panels of Figure 1 and figure 2, respectively). The RTDDFT technique does include the ground state correlation by way of the correlation and exchange functional.…”

“…This type correlation is very well documented. It can be accounted for by various theoretical approaches such as the random phase approximation with exchange (RPAE) (Amusia 1990) and its relativistic implementation (RRPA) (Johnson and Lin A c c e p t e d M a n u s c r i p t 1979), the multi-channel multi-configuration Dirac-Fock method (MMCDF) (Tulkki 1993), the relativistic time-dependent density functional theory (RTDDFT) (To↵oli et al 2002a) and, most recently, by the multi-configuration Tamm-Danko↵ (MCTD) method (Aarthi et al 2014). In the relativistic formulation, photoionization of the ns shell leads to the two spin-orbit split continua Ep 1/2 and Ep 3/2 , each of which is supported by its own scattering phase and the spherical harmonic.…”