Autoionizing resonances in the photoionization of ground state atomic magnesium

Photoionization of the ground state 1s(2)2s(2)2p(6)3s(2) S-1 Of atomic magn esium is studied theoretically in the energy legion between the Mg+(3s) and Mg+(4p) thresholds using the noniterative variational R-matrix method comb ined with multichannel quantum defect theory at the R-matrix surface. The i nitial and final states are represented by configuration-interaction wavefu nctions. We calculated total and partial photoionization cross sections in both length and velocity formulations. Photoionization cross sections are d ominated by Rydberg series of autoionization resonances converging to Mg+(3 p, 4s, 3d and 4p) thresholds. We also calculated the photoelectron angular distribution asymmetry parameter beta for the process leaving the ion in th e Mg+(3p) state. The present photoionization cross sections are in good agr eement with available experiments and previous calculations. There is excel lent agreement between length and velocity gauges in our calculation.