Laser photoionization of polarized Ar atoms produced by excitation with synchrotron radiation

The laser-synchrotron radiation combination technique has recently been incorporated into an apparatus for two-dimensional photoelectron spectroscopy of atoms and molecules in order to investigate photoionization dynamics of polarized atoms. Ground state Ar atoms are excited with linearly polarized synchrotron radiation to Rydberg states lying below the first ionization potential. The aligned atoms thus formed are ionized by irradiation of a laser which is also linearly polarized. Photoelectrons emitted in the direction of the electric vector of the synchrotron radiation are sampled and energy analysed. The photoelectron angular distribution is measured with respect to the electric vector of the laser. Expressions which correlate the asymmetric coefficients for the angular distribution with theoretical dynamic parameters involving transition dipole matrix elements are derived. The anisotropy of the present angular distribution can be reasonably explained, assuming that the matrix elements and phase shift differences are essentially independent of the total angular momentum quantum number of the final state and that the spin-orbit interaction in the continuous spectrum is small. (author)