Enhanced Nondipole Effects in Low Energy Photoionization

It is found that electric-dipole--electric-quadrupole $E1$- $E2$ interference effects at low photon energies, of the order of tens of eV, in photoelectron angular distributions can be significant, comparable to, or even larger than, effects at energies of hundreds to thousands of eV, owing to quadrupole autoionizing resonances. This is illustrated both for Ne $2p$ photoionization around 51 eV and Ar $3p$ photoionization around 33 eV, where random phase approximation with exchange calculations are performed with allowance for correlations in both dipole and quadrupole channels.