EXPERIMENTAL AND THEORETICAL CROSS-SECTIONS FOR PHOTOIONIZATION OF METASTABLE NE-ASTERISK(3S P-3(2), P-3(0)) ATOMS NEAR-THRESHOLD

Using high-resolution laser photoelectron spectrometry we have determi ned for the first time absolute cross sections sigma(J0J1) and the ele ctron angular distribution parameter beta(J0J1) for one-photon ionizat ion of metastable Ne(3s P-3(J0), J(0) = 2, 0) atoms to the resolved N e+(P-2(J1), J(1) = 3/2, 1/2)) ion states near threshold (lambda = 244 nm) as well as the beta-parameter for metastable He (2(3)S(1), 2(1)S( 0)) atoms at lambda = 244, 257.25 nm. For comparison with present and future experimental data we have calculated partial cross sections and beta-parameters for photoionization of Ne(3s, J(0) = 2,0), and of th e analogous alkali atom Na(3s) over the photoelectron energy range 0-1 0 eV. We have used both a term-dependent Hartree-Fock approach and a c onfiguration-interaction method involving Pauli-Fock atomic orbitals ( CIPF); the latter was designed to take into account the important elec tron correlation effects which are found to be essential for obtaining good agreement between the theoretical and experimental results.