Using a crossed atomic and laser beams set-up with mass spectrometric ion detection we have studied the photoionization of laser-excited, aligned Ar*(3p54p3D3) atoms from the Ar+(2P3/2) threshold up to photoelectron energies of ε = 0.846 eV. Absolute cross sections are reported for parallel (η = 0°) and perpendicular (η = 90°) polarization directions of the linearly polarized exciting and ionizing CW lasers over the range ε = 0-0.2 eV. The cross sections exhibit nd′(J = 2, 3) autoionization resonances whose combined appearance varies with angle η; this behaviour is traced to the η dependence of the partial cross sections for the final (ion + electron) channels with different total angular momentum, J1. Using theoretical formulae whose derivation is outlined we determine the energy dependence of these partial cross sections from least squares fits to the data measured at η = 0° and 90°. Experimental results are also presented for the asymmetry function, ALD(η), which describes the linear dichroism for the photoionization of aligned Ar*(4p3D3) atoms, and for the full η dependence of the ionization cross section as obtained for 10 selected photoelectron energies in the range (0.017-0.846) eV. Many-electron calculations have been carried out which provide additional insight into the photoionization dynamics. In contrast to the situation for Ne*(3p, J = 3), photoionization of Ar*(4p, J = 3) is not well described by just two reduced matrix elements Ds, Dd. For Ar* the term dependence of the Hartree-Fock wavefunctions and correlation effects lead to substantial differences between the reduced matrix elements for the five d-wave channels associated with the Ar+(2P3/2) formation. Satisfactory overall agreement is observed between the experimental and theoretical cross sections and their polarization dependence. The calculations also provide information on the weak g-wave contributions and on the cross section for leaving the ion in the excited Ar+(2P1/2) level; the latter amounts to about 1% relative to Ar+(2P3/2) formation in agreement with experimental and MQDT estimates.
|Number of pages||23|
|Journal||Journal of Physics B: Atomic, Molecular and Optical Physics|
|Publication status||Published - 1997 Feb 14|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics