Experimental and theoretical cross sections for photoionization of metastable atoms near threshold

Using high-resolution laser photoelectron spectrometry we have determined for the first time absolute cross sections and the electron angular distribution parameter for one-photon ionization of metastable atoms to the resolved ion states near threshold as well as the -parameter for metastable atoms at , 257.25 nm. For comparison with present and future experimental data we have calculated partial cross sections and -parameters for photoionization of , and of the analogous alkali atom over the photoelectron energy range 0 - 10 eV. We have used both a term-dependent Hartree - Fock approach and a configuration-interaction method involving Pauli - Fock atomic orbitals (CIPF); the latter was designed to take into account the important electron correlation effects which are found to be essential for obtaining good agreement between the theoretical and experimental results. .