Electric-dipole–quadrupole interference of overlapping autoionizing levels in photoelectron energy spectra

We have measured the photon energy dependence of electric-dipole–quadrupole interference in cadmium between the odd parity 4d⁹5s²5p J=1 and even parity 5p6p³P₂ autoionizing levels. The resonant interference structure is isolated by taking the difference between constant ionic state spectra at 45° with respect to the photon beam in the forward and backward directions. We find interference effects that are approximately 0.5% of the dipole cross section for photon energies of 13 eV, in good agreement with theory. We compare the results with those from (e,2e) experiments.