Photoelectron Angular Distributions from Polarized Ne* Atoms near Threshold

Photoelectron distributions of the polarized 2p53d Rydberg states of neon have been studied with a newly built velocity map imaging analyzer. The atoms were polarized by absorption of synchrotron radiation and ionized by an infrared laser. The asymmetry parameters β2 and β4 characterizing two-photon resonant ionization have been extracted from the measured images and compared with the results of a quantum defect treatment. To achieve a good theoretical description of the data, it is necessary to take into account the dependence of the dipole transition matrix elements and phases of the partial waves on the angular momentum quantum numbers pertaining to various continuum channels.