A determination of the angular distribution parameter beta of the atomic chlorine 3s photoelectrons over the photon-energy range from 29 to 70 eV has been carried out using electron spectrometry in conjunction with synchrotron radiation. Our results confirm the basic theoretical predictions that beta, for s-subshell photoionization in open-shell atoms, is in general term and photon-energy dependent, in contrast to closed-shell atoms where beta is always 2 nonrelativistically. However, our measurements of beta for the Cl+ 3s((1,3)P) channels demonstrate that significant details are not handled well by simple Hartree-Fock theory.
We have measured strongly negative P values of the 3s-participator lines at the magnesium 2p~4s and 2p, iz~3d excitations. Observed P values of the spectator lines following 2p~4s excitation are not reproduced by the strict spectator model. Our multiconfiguration Dirac-Fock calculations show that the resonant Auger spectra are influenced by unusually pronounced configuration interaction in the excited state. This influence is strongly enhanced by a change of sign in the Auger amplitude of the leading term near the transition energy, a dynamic effect similar to a Cooper minimum in photoionization.PACS number(s): 32.80.Hd, 31. 20.Tz, 31. 90.+s In contrast to photoemission, Auger decay takes place at a fixed kinetic energy of the outgoing electron. Thus direct tests of the kinetic-energy dependence of the Auger amplitudes are not possible. Nevertheless, variation of the Auger emission amplitudes with excitation energy can manifest itself in experimentally observable effects. Examples are the postcollision interaction between a photoelectron and an Auger electron [1] and intensity variations in the radiationless decay of photoionization satellite states differing in the n-quantum number of an outer excited electron [2]. We found another manifestation of these dynamical variations in the investigation of resonant Auger decay of 2pphotoexcited Mg. In the decays of the Mg 2p '4s excited state the Auger amplitude due to the leading configuration has a sign change very near the transition energy, similar to a Cooper minimum in photoionization [3]. This induces a strongly enhanced sensitivity of these decays to configuration interaction (CI) in the intermediate state. Theoretical [4 -6] and experimental [7 -11]studies of the angular anisotropy of resonant Auger decay have become feasible only recently. Resonant Auger lines are commonly classified as either participator lines, where the excited electron takes part in the decay, or spectator lines, in which it is not involved. A successful theoretical interpretation of the salient features of resonant Auger spectra has been possible within a single-configuration model for all rare gases [4,5], in particular the 2p excitations of Ar, while the effects of CI have been moderately small [6]. The present experimental study of the resonant Auger decay of atomic Mg following 2p~4s, 3d excitation and the theoretical analysis of the angular distributions of the pertinent resonant Auger lines by our multiconfiguration Dirac-Fock (MCDF) calculations are in remarkable contrast to this general trend.In the present case the resonant Auger decay can be treated as a two-step process, since the resonantly enhanced intensity is an order of magnitude larger than the nonresonant intensity [12] and the bandpass of the photon beam is much larger than the natural lifetime of the intermediate state Permanent address: Institute of Nuclear Physics, Moscow State University, 119 899, Moscow, Russia. excluding resonant Raman-like behavior [13].Thus, the angular distribution of the emitted electrons a...
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