Table of contents

Cross sections for one-electron capture, excitation and ionization in proton-oxygen collisions are calculated by the two-centre atomic orbital expansion close-coupling method. The transition probabilities are constructed from a one-electron independent-particle approximation. The electronic states in oxygen are represented by orbitals obtained from an analytical model potential with parameters fitted to the Hartree potential of the ground state configuration. Capture cross sections are dominated by the 2p electrons and are in very good agreement with measurements.

The direct 5p photoionization of atomic Lu has been investigated by photoelectron spectroscopy in combination with monochromatized synchrotron radiation. Binding energies of the multiplet states have been determined from the photoelectron spectra. For the interpretation of the multiplet structure, we performed Hartree-Fock calculations, where configuration interaction was taken into account. The main result is that the splitting of the multiplet structure is dominated by the spin-orbit interaction.

Using the crossed-beams technique, we have measured absolute cross sections for the total production of in collisions between and ions

by means of a beam-pulsing method for the detection for centre-of-mass energies between 1.4 and 39.8 keV. From the measured data cross sections for the electron detachment process

were calculated using the total cross sections for mutual neutralization measured previously. The electron detachment results are in very good agreement with recent theoretical calculations.

The quantum dynamical evolution of atomic and molecular aggregates, from their compact to their fragmented states, is parametrized by a single collective radial parameter. Treating all the remaining particle coordinates in d dimensions democratically, as a set of angles orthogonal to this collective radius or by equivalent variables, bypasses all independent-particle approximations. The invariance of the total kinetic energy under arbitrary d-dimensional transformations which preserve the radial parameter gives rise to novel quantum numbers and ladder operators interconnecting its eigenstates at each value of the radial parameter.

We develop the systematics and technology of this approach, introducing the relevant mathematics tutorially, by analogy to the familiar theory of angular momentum in three dimensions. The angular basis functions so obtained are treated in a manifestly coordinate-free manner, thus serving as a flexible generalized basis for carrying out detailed studies of wavefunction evolution in multi-particle systems.

We express the detachment cross section caused by a Gaussian pulsed laser in terms of that caused by a continuous laser. Using this expression and Poisson's summation formula, we derive a uniform semiclassical formula for the cross section of pulsed-laser photodetachment of a hydrogen ion in static parallel electric and magnetic fields. The uniform semiclassical formula does not have a divergence problem at the bifurcation points. Numerical comparisons show an excellent agreement between the uniform semiclassical formula and the quantum formula for the detachment cross section.

Calculations of the electronic energy loss and the straggling of the energy loss for slow single-centre projectiles in the degenerate electron gas are reported. The Hartree-Fock-Slater description of the projectile (few bound electrons) and the density function formalism (many electrons) together with the dielectric function method are used. The stopping and straggling effective charges for the energy loss are analysed and found to differ from each other and to depend on the one-electron radius , on the projectile atomic number and on the number of electrons carried by the projectile. Results of calculations are compared with available experimental data and a good agreement is found.

Channelled ions in a Si single crystal see a very high density quasi-free electron gas and hence provide an opportunity to study e-impact ionization of the projectile even though the e-e interaction responsible for this is much weaker than the e-n interaction which usually dominates the process of projectile ionization. The e-e interaction has been experimentally identified through the observed fast increase in the impact energy dependence of the ionization of the hydrogen-like F ions, the calculated contribution from the e-n interaction being impact energy independent at large impact parameters. The relative variation of the measured cross sections for well-channelled ions is in good agreement with the convergent close-coupling theory of e-impact ionization and existing scaling laws. In addition to the M-shell electrons, participation of the Si L-shell in the ionization of the channelled ion is suggested.

We have calculated total and single differential cross sections for electron impact ionization of using a method that combines the distorted-wave Born approximation for the incident/scattered electron with an R-matrix treatment of the system. Our calculation included eight states of the final ion, namely , and six states with the configuration , and up to the -pole component of the interaction between the ionizing electron and the target. The single differential cross sections exhibit considerable structure due to autoionizing resonances, including a large resonance due to the quasi-bound state . In the calculation of the total cross section, a modification to the usual half-range approximation is proposed, which ensures that the contributions from autoionizing resonances have the correct thresholds. Our theoretical results for the total cross section are in good agreement with the experimental results.

The mechanism of a gas phase proton transfer reaction, , has been investigated by means of quasi-classical trajectory calculations with an ab initio fitted potential energy surface. In particular, we focused our attention on the selectivity of vibrational and rotational states of the product OH formed by the reaction. It was found that vibrational and rotational state distributions of the product OH can be deconvolved by two components originating from two different reaction channels. One is a complex formation channel in which the trajectory proceeds via a long-lived intermediate complex [OHF]. The other is a direct channel in which the trajectory proceeds without complex formation. It was concluded that collinear and near-collinear collisions lead to the direct channel, whereas side-attack collision and collision with a large impact parameter lead to the intermediate-complex channel.

Close-coupling (CC) calculations of electron-ion recombination cross sections using the R-matrix method are presented and benchmarked with available experimental measurements. The electron-ion recombination process, including resonant and non-resonant recombination may be unified as a natural extension of the coupled-channel approximation, as traditionally employed for photoionization and electron-ion scattering. Recombination cross sections can be calculated to the same accuracy by employing similar eigenfunction expansions for the target ion. Detailed results are obtained for electron recombination with C V, C VI, O VIII and Fe XXV. Several sets of theoretical calculations are reported and discussed: non-relativistic CC in LS coupling, relativistic CC in the Breit-Pauli approximation, with radiative attenuation and fine structure, and the relativistic distorted-wave approximation. The theoretical results are in very good agreement with highly accurate experimental measurements at the Heidelberg test storage ring for C V, C VI and O VIII, and the electron-ion beam trap at Livermore for Fe XXV. We discuss the overall effect of radiation damping of all resonances on effective cross sections and rates, important for H- and He-like ions. In addition to agreement with experimental data, the validity of the CC calculations is demonstrated by the continuity between the calculated photorecombination, dielectronic recombination and electron impact excitation cross sections. Certain issues related to the works of Badnell et al (1998 J. Phys. B: At. Mol. Opt. Phys. 31 L239) and Robicheaux (1998 J. Phys. B: At. Mol. Opt. Phys. 31 L109) are also addressed.

The first sideband Raman excitations driven by counter-propagating Raman beams are analysed for the trapped ion under the localization condition in or beyond the Lamb-Dicke regime. It is demonstrated that multiquantum processes in the vibrational couplings produce significant effects on the the first sideband Raman transitions and the relevant Raman displacements for the trapped ion beyond the Lamb-Dicke regime. The quantum features of the vibrational states attained by displacing the motional ground state are demonstrated to be closely associated with the nonlinear vibronic couplings. Quantum entanglement, and quantum interference as well, are discussed for ion traps with various Raman excitation and localization conditions. The results are compared with the recent experiment reported by Monroe C et al in 1996 Science 272 1131-5.

We derive a parametrized formula for the photoionization cross section in the vicinity of an autoionizing state (AIS) coupled with another AIS by a strong laser field. The rotating-wave approximation is used and adiabaticity is assumed. In the probe field spectrum two Fano resonances contribute to the cross section, while a single resonance occurs in the strong-field spectrum. The correlation between the resonance shape and the complex energies of the laser-driven two-level system is described. Calculations are performed for the and AIS pair in He and for the and pair in Mg. The results agree with those obtained using time-dependent approaches. The formula for the cross section describes the spectral features of the ion yield measured in the two-photon ionization of the Mg atom via the AIS coupled with the state. The appearance of laser-induced degenerate states in the cross section shape is studied.

A threshold photoelectron spectrum and its component spectra of Auger cascades following Kr -shell photoionization have been measured by a threshold photoelectron-ion coincidence technique. These spectra exhibit characteristic profiles of post-collision interaction effects induced by the Auger cascades. Peak shifts of the profiles increase gradually according to the times of the interactions, but peak widths of the profiles are almost independent of the times of interactions. These characteristics are analysed in terms of a simple model based on the assumption that double-Auger (Auger shake-off) decays reduce the effective number of steps of the Auger cascades.

The valence shell binding energy spectra and three inner valence orbitals electron momentum distributions for propane are measured by symmetric non-coplanar electron momentum spectroscopy at an impact energy of 1200 eV. The measured binding energy spectrum is compared with previously published results. The experimental momentum profiles of three inner valence orbitals are compared with calculated momentum profiles by Hartree-Fock and density functional theory (DFT-B3LYP) methods using double-zeta and 6-311++ basis sets. Agreement is found between experimental and calculated results. The position and momentum space density maps for three inner valence orbitals of oriented molecule are presented.

Charge transfer cross sections for collisions of ground state and excited state ) with atomic helium are presented for energies less than 250 eV . Using a fully quantum mechanical, molecular-orbital, close-coupling approach, the cross sections are calculated in a diabatic representation. Completely ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained with the spin-coupled valence-bond method are utilized. Rate coefficients for temperatures between 100 and 100 000 K and cross sections for collisions with isotopic are presented. Results for the reverse process, , are also given.

An isotropic temperature-dependent intermolecular potential is proposed for simultaneous prediction of the second virial coefficient B and the viscosity of over a wide temperature range. Potential parameters at 0 K (repulsive power n = 24.28, equilibrium distance , potential well depth K) and the enlargement of the first excited state are determined by solving an inverse problem of minimization of the sum of squared deviations between calculated and measured data normalized to the relative experimental error. The temperature dependence of the average excited state parameters and is implied in the temperature dependence of the effective excited state enlargement calculated via the vibrational partition function. Tables with recommended potential parameters, second virial coefficient, viscosity and self-diffusion in a temperature range of 175-900 K are proposed.

The satellite spectrum of silicon is reported. It is found to consist of three lines at 1891.4, 1896.7 and 1903.0 eV. These have been assigned to the - group of transitions. The transition array has been, for the first time, analysed in terms of ten components as against the four reported in the literature. The relative contribution of each of the ten components in emitting these lines has been estimated and hence these lines have been identified as , and satellites, respectively. A weak structure at 1885.0 eV, in addition to the - spectrum, has also been observed and has been tentatively assigned to a - hypersatellite transition. The energy level diagram for the , and levels has also been presented.

We investigate the electronic structure of the helium atom in a magnetic field between B = 0 and . The atom is treated as a nonrelativistic system with two interacting electrons and a fixed nucleus. Scaling laws are provided connecting the fixed-nucleus Hamiltonian to the one for the case of finite nuclear mass. Respecting the symmetries of the electronic Hamiltonian in the presence of a magnetic field, we represent this Hamiltonian as a matrix with respect to a two-particle basis composed of one-particle states of a Gaussian basis set. The corresponding generalized eigenvalue problem is solved numerically, providing results for vanishing magnetic quantum number M = 0 and even or odd z-parity, each for both singlet and triplet spin symmetry. Total electronic energies of the ground state and the first few excitations in each subspace as well as their one-electron ionization energies are presented as a function of the magnetic field, and their behaviour is discussed. Energy values for electromagnetic transitions within the M = 0 subspace are shown, and a complete table of wavelengths at all the detected stationary points with respect to their field dependence is given, thereby providing a basis for a comparison with observed absorption spectra of magnetic white dwarfs.

We apply the strong-field S-matrix theory to the above-threshold ionization (ATI) in a bichromatic linearly polarized laser field having frequencies and , and the relative phase between the laser field components. The presented theory includes both the Coulomb and rescattering effects. We compute and discuss the electron energy spectra for different angles between the momentum of the ionized electron and the polarization vector of the laser field. We found that the plateau for and for the backward emission of electrons extends up to , where is the ponderomotive energy of the first laser field component (assuming equal intensities of both components). There are no such high-energy electrons for , in contrast to the symmetry , valid in the monochromatic case. In the bichromatic case the ionization rates possess the more general symmetry property . Therefore, for we predict the emission of the high-energy electrons in the forward direction . In a bichromatic field the sidelobe structures are strongly influenced by quantum mechanical interference effects. We also explore the -dependence of the ionization rates for different relative phases , and for those energies which correspond to the classical cutoff law.

Mass polarization arises from a correlation between electronic momenta. In Li-like systems, the effect of core electron correlation dominates. The mass polarization for the and states in B III-Ne VIII is calculated with the use of configuration interaction (CI) wavefunctions. Its dependence on the nuclear charge Z and the atomic states is then studied. The effect of core electron correlation is clearly illustrated with a simple CI wavefunction.

Simple analytic expressions are obtained for relativistic electron energies and angular distributions produced in tunnelling ionization of atoms by intense laser radiation. Circularly polarized radiation is considered, using the Landau-Dykhne approach. Major differences have been found as compared with the previously investigated case of linearly polarized laser radiation: a circularly polarized intense field produces mainly relativistic electrons, while a linearly polarized intense field produces mainly non-relativistic electrons. In the limit of a weak field we obtain well known expressions for the non-relativistic energy spectrum and angular distribution of ejected electrons in the tunnelling ionization of atoms. (Limited, of course, to the case where the so-called Keldysh parameter corresponds to the tunnelling regime of ionization.) Simple expressions have been found for: (1) the angle between the direction at which most of the relativistic electrons are ejected and the plane of polarization of the laser radiation; (2) the energy spectrum at this angle; (3) the width of the energy spectrum and the position of its maximum; (4) the angular distribution near this angle and the width of this distribution. Our simple purely analytical results for energy and angular distributions are in agreement with the numerical derivations of Reiss based on the strong field approximation.