Table of contents

Measurements of the triple differential cross section for inelastic photon scattering from bound atomic electrons are reported. The experiment was done using 148 keV synchrotron radiation from the DORIS storage ring at DESY, Hamburg. The target was an 80 nm thin Cu foil.

The authors report experimental results demonstrating that the friction force acting on atoms in a bichromatic standing light wave can substantially differ from that in a monochromatic standing wave. Even a sign reversal can occur in a laser frequency range depending on the spatial phaseshift between the two standing wave components.

The fluxes across the phase-space bottlenecks are treated in the first order of classical perturbation theory and simple formulae are derived for the bottlenecks formed by broken quasiperiodic and homoclinic orbits. These formulae are applied to the model problem of HeI₂ vibrational predissociation and good agreement between the first-order and exact fluxes across unperturbed bottlenecks is found. Perspectives of the first-order approach in the framework of the kinetic description of phase-space transport are drawn.

The predictions of the multichannel eikonal theory (MET) and two distorted wave theories are considered for the sigma _{11S not=31D} integral cross section and the Stoke parameters P_i (i=1,2,3) for the 3¹D state of He at intermediate energies. Significant differences are found between the distorted wave and multichannel eikonal theories for the Stokes parameters in the case where the dipole couplings 2¹P_m to 3¹D_m' and 3¹P_m to 3¹D_m' are omitted in the solution of the coupled equations of the eikonal theory. Switching off the electric dipole transitions coupling the 2¹P_m and 3¹P_m states to the 3¹D_m' substates in the MET changes the underlying MET complex scattering amplitudes for the 3¹D_m' magnetic substates in such a way that the resultant sigma _{11S not=31D} integral cross section for the excitation of the 3¹D state of He drops by a factor of between 5 and 8 for incident electron energies E between 30 and 60 eV.

The authors extend their previous work on the closed form expression for the negative order hydrogenic dipole sum rules in three dimensions to arbitrary multipoles and arbitrary dimensions.

For a range of Woods-Saxon potentials the breadth Gamma of shape resonances is shown to be related to the resonance energy E_res relative to threshold by Gamma = gamma E_res^x, where x and gamma are strongly angular momentum dependent. Such a power law holds for a much wider range of energy than would be expected theoretically, and forms a useful limiting relation for understanding shape resonance and giant resonance phenomena in a variety of physical systems, including atoms, nuclei and atomic clusters.

The authors have considerably extended their earlier configuration interaction calculations of the emission A-values of transitions from the 2p3s ¹P⁰ and 2s2p³¹P⁰ levels. Their results are in good agreement with other, quite different, calculations, but their calculated lifetime of 0.218 ns is significantly higher than the experimental value of 0.17+or-0.01 ns obtained using the beam-foil-laser method.

The parameter-free exchange potential of Gaspar (1974) has been applied to determine excitation energies of Na and K atoms. The calculations have been done with the fractional-occupation approach of the density functional theory formulated by Gross et al. (1988).

For atomic media with resonant Doppler-broadened transitions of J=0 to J'=1 or J=1 to J'=0 type and taking into account the relaxation due to depolarizing collisions a theory of nonlinear magneto-optic polarization phenomena is developed. The theory is valid in the case of both arbitrary resonance linearly-polarized radiation intensity and arbitrary external magnetic field spatial orientation. The Faraday and Voigt geometries are analysed in detail, and in the case of the Faraday geometry the effect is considered of a noncompensated magnetic field transverse component on the shape of a dependence relating the radiation polarization plane rotation angle to a magnetic field longitudinal component. In the case of the Voigt geometry an essential effect is found of the angle between the radiation initial polarization and transverse magnetic field vectors on the character of the dependence relating the radiation polarization plane rotation angle to the transverse magnetic field magnitude.

The collisional broadening and shift of the fine structure lines of Ca (4s4p(³P⁰)-4s5s(³S)) perturbed by hydrogen atoms are calculated in a quantum mechanical approach for a wide range of temperatures (4000-5000 K). These results are based on potential energy curves newly calculated in a method which gives a very good description of the electronic states in both the asymptotic region (separated atoms Ca+H) and the molecular region. The results when compared with the usual Van der Waals approximation (asymptotic part of the potential only) show significant discrepancies arising from both the contribution of the intermediate part of the potentials and the effect of the fine structure coupling.

6p₃2/nl (n=11 to 15, l=5 to n-1) and 6d₅2/nl (n=11 to 14, l=6 to n-1) doubly excited Rydberg states of barium have been studied using a multistep laser excitation technique. The excitation is via the bound 6s₁2/nl states which are populated using an electric-field switching method which allows the selective population of high-l angular momentum states. The resulting spectra clearly demonstrate the presence of dielectronic correlation. The authors show that this correlation is well described in terms of the (j-l)K coupling scheme, taking into account in a perturbative way the dipole and quadrupole interaction terms.

The R-matrix method has been applied to calculate photoionization cross sections for the 2s²2p³⁴S⁰ ground state of the N-like Al⁶⁺ ion. To test the accuracy of results, calculations are carried out in the LS coupling scheme with two sets of target states and results were obtained in both the length and velocity formulations. In the first, the six target states, ³P^e, ⁵S⁰, ³D⁰, ³P⁰, ³S⁰ and 2p⁴³P^e, are constructed by using 1s, 2s and 2p atomic orbitals. In the second set these states are represented by extensive configuration interaction using 3s, 3p and 3d correlation orbitals in addition to the spectroscopic ones. The partial and total cross sections are obtained. The cross sections are dominated by Rydberg series of resonances converging onto higher thresholds of Al⁷⁺. Some prominent resonances have been analysed and their positions and widths are listed.

The angular distribution of Auger electrons in the decay of resonantly excited atomic states is studied theoretically. The two-step model is used for a description of the Auger process with the excited electron as a spectator. Expressions for the angular anisotropy parameters in the jK and jj coupling schemes are obtained for excitation of a closed-shell system. A close relation between the angular anisotropies of the resonant Auger and normal Auger processes is found within the framework of the spectator model. Numerical calculations for resonant Auger transitions in Ar, Kr and Xe are presented and compared with recent experiments.

The constant residual energy-loss spectra for the case of the 5d⁹6s²(²D_3/2)6p₁2/(3/2 1/2)₂ state in Hg are calculated. These spectra were observed in the process of the electron impact excitation and following decay of autoionizing state. The distortions resulting from the post-collision interaction (PCI) are taken into account. The comparison with the experiment permits to evaluate the autoionizing state width Gamma =9.9 MeV and the parameters of the angular distribution of the autoionizing electrons.

The averages of the electric and magnetic fine structure interaction operators for the nonpenetrating Rydberg states in diatomic molecules for four different Hund coupling d cases are obtained. A method which allows the author to avoid operations with the nondiagonal matrix elements is used. It is shown that in the d cases the differences between the levels of the electric fine structure satisfy the rule Delta E=E_N+1^EFS-E_N^EFS=G₁(N+1)³-G₂(N+1), where N is the total momentum without the spin and G₁ and G₂ are constants. It is shown that the recent experimental data for H₂, He₂ and NO are in good agreement with the theoretical results.

Using circularly polarized synchrotron radiation, the 5p pi ionization of HI molecules is studied by means of angle-resolved photoelectron spin polarization spectroscopy. The energy dependences of the dynamical photoionization parameters are obtained and compared with an ab initio calculation of Raseev et al. (1987) and the corresponding data for the xenon atom. Angular distributions of the polarization component A( Theta ) yield complete parameter sets. A strong influence of electronic autoionization is observed and analysed in terms of partial contributions using the additional information contained in the polarization results.

Absolute photoabsorption cross sections for sulphur dioxide have been measured in the VUV region from 147 to 1017 AA. By the use of a windowless double ion chamber, the authors have been able to achieve accuracies between +or-1 and +or-2%. The results are compared with the only two published cross section data in this wavelength region. All three measurements agree well in the short-wavelength region but differ by up to 25% at wavelengths longer than 300 AA.

Based on a comprehensive set of transport parameters of electrons in methane derived from single electron spectra in the range of field 0.01-15 Td the authors determined a set of elastic and inelastic scattering cross sections up to 3 eV. The necessity to include anisotropic elastic scattering in a Boltzmann analysis of methane is demonstrated. In addition the drift velocity in a mixture of methane with helium was used to enhance the reliability of the derived cross sections. The low energy part of the cross sections for elastic scattering is subject to a MERT analysis and is compared with total cross section data from single scattering experiments.

Time-of-flight detection of neutral metastable fragments has been applied to the study of electron-impact dissociation of CF₄ molecules. The time-of-flight distributions indicate that a number of distinct processes are involved in the production of metastable fragments. Excitation functions for these processes have been measured up to 400 eV. The results presented are compared with other studies of fragmentation of CF₄ and indicate that fragmentation into an excited CF₃⁺ ion and an excited F atom is a prominent process.

Resonance ionization spectroscopy in collinear geometry has been successfully applied to a fast beam of ytterbium atoms. The atoms were excited stepwise into a Rydberg state by pulsed laser light, ionized in an electrical field and deflected onto a secondary electron detector. The efficiency was 1*10^-5 detected ions per incoming atom on a background from collisional ionization of 1*10^-8. The technique has been exploited for the measurement of hyperfine structures and isotope shifts of unstable ytterbium isotopes, in particular ¹⁵⁷Yb, ¹⁵⁹Yb and ¹⁷⁵Yb.

Using Doppler-free two-photon excitation from the ground state 4f¹⁴6s²¹S₀ the even-parity J=2 levels of the 4f¹⁴6s7d and 4f¹⁴6s8d configurations as well as the 4f¹⁴6p², 4f¹³6s²6p and 4f¹³5d6s6p configurations between 44760.4 and 47341.8 cm^-1 in neutral ytterbium have been investigated with regard to the hyperfine structure of the excited states and the isotope shift of these transitions. The experimental results for the hyperfine splitting constants have been analysed regarding possible singlet-triplet and configuration mixing. The experimental values have been compared with theoretical results obtained in an ab initio calculation. A strong influence for the second-order hyperfine interaction could be established in both the 4f¹⁴6s7d ³D₂ and the 4f¹⁴6s10s ¹S₀ states.