We have investigated the collisional excitation of hydrogen atoms by protons and multiply charged ions at intermediate velocities applying the optical method. The population or the np levels (n = 2,. . . ,6) has been determined for a variety of projectiles with charge states q ranging from I + to I I + and scaled velocities U/& between 0.7 and 5.6au. The cross &ions are shown to fulfil the scaling relation o / q = f ( d / q ) with respect to the projectile charge q and velocity U for q>3. The relevan= of scaled intermediate velocities for a classification o f excitation mechanism is pointed out.

The Kr 4s-electron photoionization cross section as a function of the excitingphoton energy in the range between 30 eV and 90 eV was calculated using the configuration interaction (CI) technique in intermediate coupling. In the calculations the 4p spin-orbital interaction and corrections due to higher orders of perturbation theory (the so-called Coulomb interaction correlational decrease) were considered. Energies of Kr n states were calculated and agree with spectroscopic data within less than 10 meV. For some of the Kr 11 states new assignments were suggested on the basis of the largest component among the calculated CI wavefunctions.

Absolute cross sections for the transitions of the Kr atom into the 4s land 4p4nl states of the Kr + ion were measured in the 4s-electron threshold region by photon-induced fluorescence spectroscopy (PIFS). The cross sections for the transitions of the Kr atom into the 4sland 4p4nl states were also calculated, as weIl as the 4p4nln'I' doubly excited states, in the frame of LS-coupling many-body technique. The cross sections of the doubly-excited atomic states were used to illustrate the pronounced contributions of the latter to the photoionization process, evident from the measurements. The comparison of theory and experiment led to conclusions about the origin of the main features observed in the experiment.

Photon-induced fluorescence spectroscopy was applied for the first time to investigate the anisotropy of VUV radiation emitted from Kr II satellite states with total angular momentum J 3 2 after the photoionization of the Kr atom by linearly polarized synchrotron radiation near the 4s threshold. The measurements showed that the sign of the alignment parameter is practically independent of the exciting-photon energy for the ionic state with J = 5 2 , whereas for the states with J = 3 2 the alignment parameter changes sign with varying energy. Simple formulae connecting the angular distribution parameter and the alignment parameter with the kinematics of our experiment and with quantities describing the dynamics of the photoionization were derived in closed form. Partial and total cross sections for the photoionization of 4p, 4s and several satellite levels were calculated taking into account many-electron correlations and doubly-excited states. For the satellite states with J 3 2 the dependence of the angular distribution parameter on the exciting-photon energy was calculated. Good overall agreement between theory and experiment was obtained.

The energy dependence of the alignment parameter A20 for the Kr II 4p45p(E 1J1) states following excitation in the Raman regime with the exciting-photon energy passing through the Kr I 3dJ̄9npj̄ resonances was investigated theoretically and experimentally. Interference between the resonance and direct photoionization channels explains the dependence of A20 on the excitation energy. Experimentally, A20 was determined after the analysis of 5p–5s fluorescence decay of the 4p45p(E 1J1) states excited with monochromatized synchrotron radiation. The band pass of the synchrotron radiation was set to 10 meV which is smaller than the natural width of the 3d9np resonances (∼83 meV). Additionally, a strong energy dependence was predicted for the orientation parameter O10 as well as for the angular distribution parameter of photoelectrons, βe, for several 4p45p(E 1J1) ionic states.