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Total and partial (4d ', 4f ', 5s ', 5p ', Sd ', 6s ') cross sections of atomic Ba, La, and Ce have been determined by absorption and photoelectron spectroscopy in the range of the giant 4d~(4f, ef) resonances. Many electron theories that take polarization and relaxation effects into account describe the gross features of the spectra but in many cases fail to reproduce the exact energy positions, line shapes, and amplitudes of the resonances in the cross sections of the main and satellite lines.

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Excitation and decay of the 4d '(4, e)f giant resonances of atomic Sm, Eu, and Gd have been investigated by photoabsorption and photoelectron spectroscopy. The experimental total and partial cross sections are compared to those predicted by many-electron theories. Autoionization into the 4f 'el continuum dominates. The character of the giant resonances is closer to that of a 4d '4f resonance than to that of a 4d 'ef shape resonance encountered for Ba and La.

A new method is described in which Li atoms are excited and aligned by pumping of the Li \s 2 2s 2 S\/2-+ \s 2 2p 2 P 1/2,3/2 transitions with a linearly polarized dye-laser beam, and subsequently raised to core-excited \snln'l' 2 S, 2 P, 2 D states by linearly polarized synchrotron radiation. The intensity of the electrons ejected upon the Li \snln'l' 2 S, 2 D-+ Is 2 l Soel autoionization strongly varied with the character of the core-excited state, the intermediate 2 P\/i or 2 Psn state, and the angle between the polarization vectors of the two photon beams.PACS numbers: 32.80.Rm, 32.80.DzVacuum-ultraviolet (VUV) photoelectron spectroscopy has proven an ideal tool for studying the manyelectron dynamics of core-excited atoms. { By the combining of high-power tunable lasers with synchrotron radiation, a new field has been opened. 2 " 4 States optically inaccessible from the ground state can be reached and the ionization of excited states can be investigated. To exploit the full power of the method, we transferred the techniques developed in two-photon laser ionization 5,6 to the VUV regime. The intensity and angular distribution of the outgoing photoelectrons critically depends on the character of the core-excited state, on the alignment of the intermediate state prepared by the laser, and on the relative orientation of the polarization vectors of the two EleVl 6667 6^2 61 06 P: 539 1 85 0-00 i SR Excitation Laserj i i L} r r 1s2p 3 P L = 0.1.2 AutoionizationK 1s2s 3 S 1S 21 S0 l^vl 1s 2 2s 2 S, 3/2 FIG. 1. Schematic energy-level diagram for the Li evenparity core-excited states reached by two-photon (laser plus synchrotron radiation) excitation.radiation fields. Therefore, two-photon ionization can be used as a very sensitive probe to study the excited states of atoms. The three-electron atom Li is an excellent model system to test this new method for core-excited states. The excitation and decay channels are displayed in Fig. 1. Our results are compared with the Kabsorption spectrum of Li* ls 2 2p by Mcllrath and Lucatorto, 7 and with the assignments based on theoretical calculations. 8,9 The experimental arrangement is schematically depicted in Fig. 2. The Li atoms were prepared in an atomic beam emanating from a resistively heated stainless-steel oven. The oven was operated at 400 °C to produce a density of about 10 10 Li atoms/cm 3 in the interaction zone. The 0.6-W linearly polarized beam of a cw-ring-dye laser induced either the transition 2s 2 S\/2 Synchrotron Radiation Cold trap / Electron trajectory Spectrometer axis -CMA-Entrance slit Magic angle (54/7°) Laser radiation Polarization axis FIG. 2. Scheme of the experimental arrangement. The main axis of the polarization ellipse of the synchrotron radiation defines the z axis. The entrance slit of the cylindrical-mirror analyzer, aligned along the z axis, is schematically depicted. The synchrotron radiation propagates in the y direction, and the laser beam in the opposite direction. Both photon beams intersect the atomic Li beam propagating in the x direc...