David Keating

Relativistic calculations of angle-dependent photoemission time delay

A.S.K. acknowledges the support of the ARC Discovery grant DP120101805. V.K.D. acknowledges the support of the NSF under Grant No. PHY-1305085. P.C.D. acknowledges the support of a grant from the Department of Science and Technology, Government of India. S.T.M. was supported by the Division of Chemical Sciences, Basic Energy Science, Office of Science, US Department of Energy.

Relativistic Effects in Photoionization of Outer ns Subshells of Heavy Atoms

At high enough Z, relativistic effects become important contributors to the quantitative and qualitative nature of atomic properties. It is important to identify and study these relativistic effects as they evolve with increasing Z in order to fully understand atomic properties. The most prevalent relativistic effect is the creation of spin-orbit doublet channels and dynamic changes, i.e., changes in the wave functions, which also shifts the thresholds. The ns subshells are chosen because they do not have a spin-orbit doublet, which simplifies the study of the dynamic effects. A theoretical study of the 6s subshell of mercury (Z = 80), radon (Z = 86), radium (Z = 88) and nobelium (Z = 102) and the 7s subshell of radium and nobelium have been performed using the relativistic random phase approximation (RRPA) methodology [1]. In order to determine which features in the photoionization cross section are due to relativistic effects, calculations are performed using the (nonrelativistic) random phase approximation with exchange (RPAE) methodology [2]. The RPA methodologies were chosen because of their ability to exclude channels from the calculations. This is important because interchannel coupling can obscure and diminish the dynamic effects. Calculations are performed with and without interchannel coupling for comparisons. Without the inclusion of interchannel coupling there is a very clear difference between the RRPA and RPAE results, the absence of a Cooper minimum from the RRPA curves, which is clearly present in the RPAE results. As Z increases the Cooper minimum, in the RPAE, falls into the discrete spectrum, as can be seen in top plot of Figure 1(A). Studying the descent of the minimum into the discrete spectrum reveals that the Cooper minimum is clearly missing in the RRPA results and not just hidden in the autoionization region. Interchannel coupling pulls some of the Cooper minimum back out of the discrete, in the RPAE curve (see B plot of Figure 1), and induces one due to the coupling with the 5d subshell in the RRPA curve. The influence of the 5d subshell completely reshapes the two methodologies results into very similar cross sections. The major differences in the (B) bottom plot of Figure 1 are due to the differences between their 5d cross sections.

Confinement Effects On Spin-Orbit Activated Interchannel Coupling

The spin-orbit activated interchannel coupling is a purely relativistic effect that alters the partial photoionization cross sections of spin-orbit doublet channels. Presented is an exploration of how the spin-orbit activated interchannel coupling is affected by confinement in a C60 cage.