Strong nondipole effects in low-energy photoionization of the5sand5psubshells of xenon

Abstract

Large nondipole effects are predicted in the angular distribution of photoelectrons from the $5s$ and $5p$ subshells of xenon for photon energies below 200 eV. The nondipole parameter ${\ensuremath{\gamma}}_{5s}$ exhibits a dispersion-curve variation near the first minimum of the $5s$ cross section at 35 eV, reaching a minimum value of $\ensuremath{-}0.8$ near 40 eV. Rapid variation of ${\ensuremath{\gamma}}_{5s}$ is also found near the second minimum of the $5s$ cross section at 150 eV, where ${\ensuremath{\gamma}}_{5s}$ reaches a maximum value of 1.2. Smaller, but significant, nondipole effects are also found in the parameter ${\ensuremath{\zeta}}_{5p}={\ensuremath{\gamma}}_{5p}+3{\ensuremath{\delta}}_{5p},$ which has a maximum value of 0.15 near 50 eV, and a second maximum value of 0.18 near 160 eV. The higher energy maxima in ${\ensuremath{\gamma}}_{5s}$ and ${\ensuremath{\zeta}}_{5p}$ arise from correlation enhanced by shape resonances in the $4\stackrel{\ensuremath{\rightarrow}}{p}f$ quadrupole photoionization channels. These predictions are based on relativistic random-phase approximation calculations in which excitations from $5p,$ $5s,$ $4d,$ $4p,$ and $4s$ subshells are coupled.