On Resonance Enhancement of E1-E2 Nondipole Photoelectron Asymmetries in Low-Energy Ne 2p Photoionization

Earlier, a significant enhancement of the nondipole parameters γ2p, δ2p, and ζ2p=γ2p+3δ2p in the photoelectron angular distribution for Ne 2p photoionization was predicted, owing to resonance interference between dipole (E1) and quadrupole (E2) transitions. This enhancement manifests as narrow resonance spikes in the parameters due to the low-energy 2s→3p and 2s→4p dipole, as well as the 2s→3d quadrupole autoionizing resonances. Given the unique nature of this predicted enhancement, it requires further validation, specifically regarding whether these narrow spikes in γ2p, δ2p and ζ2p will or will not retain their values for experimental observation if one accounts for a typical finite frequency spread in the ionizing radiation. To address this, we revisit the previous study, now incorporating the effect of frequency spread in the ionizing radiation, assuming a spread as large as 5 meV at the half-maximum of the radiation’s intensity. In the present paper we demonstrate that while the frequency spread does affect the resonance enhancement of γ2p, δ2p and ζ2p, these parameters still retain quantitatively significant values to be observed experimentally. The corresponding calculations were performed using the random phase approximation with exchange, which accounts for interchannel coupling in both dipole and quadrupole photoionization amplitudes.