ANGULAR-DISTRIBUTIONS OF PHOTOELECTRONS FROM POLARIZED AR-ASTERISK(4P, J = 3) ATOMS NEAR-THRESHOLD - EXPERIMENTAL RESULTS AND THEORETICAL-ANALYSIS

Following our recent mass spectrometric study of wavelength-dependent photoionization of laser-excited, polarized Ar(4p, J = 3) atoms near threshold (1997 J. Phys. B: Ar. Mel. Opt. Phys. 30 609) we report elec tron angular distributions for photoionization of polarized Ar(4p. J = 3) atoms at four energies (epsilon = 23, 144, 316, 846 meV) above th e AR(+)(P-2(3/2)) threshold. The measurements allow us to both check t he atomic alignment produced in the optical pumping process and test i n detail results of theoretical many-electron calculations for the rel evant reduced dipole matrix elements and phase shifts. In contrast to the situation for Ne(3p, J = 3) (1983 J. Phys. B: At. Moi. Phys. 16 2 945), photoionization of Ar(4p, J = 3) cannot be simply described by two reduced matrix elements D-s and D-d and a single phase difference Delta = delta(d) - delta(s). For Ar the term dependence of the Hartre e-Fock wavefunctions and correlation effects lead to substantial diffe rences between the reduced matrix elements for the five d-wave channel s and between the five existing phase differences. The comparison of t he experimental angular distributions with those calculated theoretica lly shows that good agreement is obtained when the theoretical values of the reduced matrix elements for the d-wave channels are increased ( relative to that for the s-wave channel) by a common, energy-dependent factor; this finding is in accord with conclusions from the polarizat ion-dependent ion production data. The correction factors range from 1 .4 to 1.1 (epsilon = 23-846 meV) for calculations which include long-r ange core polarization effects, while they amount to values between 2. 0 and 1.5 when core polarization effects are neglected.