Table of contents

Calculations of e^+or--H elastic scattering phaseshifts are reported and compared with other theoretical values.

Integrated cross sections, at electron impact energies of 3.0-3.3 Ryd, for the 1S-2S transition in He⁺ are in reasonable agreement with experiments by Peart and Dolder (1973). A variant of the distorted-wave procedure is used and is briefly described. In addition, the differential cross sections for the 1S-2S transition at impact energies of 3.005, 3.010 and 3.200 Ryd are presented.

The classical three-body p-H cross sections of Abrines and Percival (1966) and of Banks (1972) for target atoms in an arbitrary uniformly-populated highly-excited level n have been improved. The results are important in the study of laboratory and astrophysical plasmas and for comparisons with the experimental p-H data of Koch and Bayfield (1975), who have investigated loss from the levels 44<or approximately=n<or approximately=50. For such values of n and higher, the classical three-body results should be accurate to within the stated statistical errors.

Cross sections for two-electron-one-photon transitions following double K-shell ionization in 200 keV collisions of N⁺+NH₃, O⁺+H₂O and Ne⁺+Ne are reported. These transitions are of the type (1s)^-2 to (2s)^-1(2p)^-1.

Collision spectroscopy of the Mg⁺-rare-gas systems has shown very different behaviour for Mg⁺-Ne compared with the other systems. This finding is discussed in the framework of the electron-promotion model. The importance of the quasi-u,g symmetry is pointed out and found to be responsible for the selectivity of the excitation processes.

A Li and Be-like Ne K Auger-electron spectrum produced by 45 MeV Cl¹²⁺ ion impact on neon with a spectroscopic resolution of 1.5 eV (FWHM) is reported. The spectral features are compared to the competing high-resolution Ne K X-ray spectrum in order to identify the spectral structure and to determine the fluorescence yield for the initial Li-like (1s2s2p) configuration in neon.

The quasimolecular M radiation emitted in collisions between Xe ions of up to 6 MeV energy and solid targets of Ta, Au, Pb and Bi, as well as a gaseous target of Pb(CH₃)₄, has been studied. Using a realistic theoretical correlation diagram, a semiquantitative explanation of the observed peak structure is given.

Line-broadening constants are calculated for the sodium D lines perturbed by He, Ne, Ar and Xe, and are compared with experimental data. Good overall agreement is found using the interatomic potentials calculated by Pascal and Vanderplanque (1974) and the collision calculation of Lewis and McNamara (1972).

The R-matrix method for electron-molecule scattering is applied to the elastic scattering of electrons from F₂ in the static-exchange approximation. Calculations are presented using both F₂ and F₂^- core orbitals to construct the interaction potential. A p_sigma -wave resonance found in the cross section is interpreted in terms of the presence or absence of a bound F₂^- ion.

Investigates the hyperfine structure of the 1s²2p ²P state of lithium using configuration interaction wavefunctions, with a view to understanding which configurations are important. In addition to single particle replacements 1s to 2s, 1s to 3d, the replacement 2p to np must also be included, even though to first-order its effect is negligible (Brillouin's theorem). The inclusion of two-particle replacements makes the coefficients of the 1s²np configurations non-zero. It is this effect which almost entirely accounts for the modification of the orbital term a_l from its Hartree-Fock value. The values of the magnetic hyperfine constants A₃2/=-3.1 MHz, A₁2/=46.2 MHz, are in agreement with experiment.

For pt.I see ibid., vol.9, p.47 (1976). A semi-empirical method developed to calculate Auger line energies within the intermediate-coupling framework has been used to determine the K-LL, K-LM, K-MM, L-LM and L-MM transition energies associated with the argon atom. Comparison with the available experimental information provides a measure of the usefulness of the method. Agreement between the theoretical predictions and the known experimental data is extremely good. For the K-LM series the present work suggests that there is a calibration error in the work of Mackey et al. (1974). Correction and reassignment provides excellent agreement between theory and experiment. The importance of configuration-interaction effects in determining line energies is also discussed.

The author shows that the interaction between excited atoms may be described by classical electrodynamic equations, provided that ground-state fluctuations are insignificant. This fact is used to investigate the resonant transfer of energy from an excited atom to an identical unexcited one, recovering and extending results obtained from a quantum treatment by Stephen (1964).

Calculations of photoionization cross sections relative to the 2p subshell have been carried out for the following atoms: Ne, Na, Mg and Al and their ions, and to the 3p subshell for the neutral atoms Ar, K, Ca and Sc and some of their ions. The ground state of the most ionized elements involves the 1s²2s²2p and 1s²2s²2p⁶3s²3p configurations. The evolution of the behaviour of the cross sections as the degree of ionization increases and a comparison of these results with others are emphasized. To remedy the failure, in some instances, of a central potential (relative to the ground state) model for neutral atoms and weakly ionized elements an alternative central potential calculated from a spectroscopic criterion and the close-coupling approximation (3p⁶ and 3p⁵ configurations) has been used.

The formalism developed for resonant scattering of electrons by molecules is used to describe the decay of an autoionizing atomic state excited by a slowly moving electron. It is predicted that the energy of the ejected electron should be shifted, as observed by the Manchester electron-scattering group. A simple calculation gives reasonable quantitative agreement with the experiments. When the scattered electron is much slower than the ejected electron, a semiclassical 'post-collision' model appears to be valid. The deviations from this model, which appear for more energetic scattered electrons, are explained as due to a screening of the ionic field by the ejected electron.

The electron detachment cross sections of H^- have been calculated semi-empirically in the energy range 2-1000 eV with and without the Coulomb effect. The inclusion of Coulomb repulsion leads to satisfactory agreement with the available theoretical and experimental data.

The Blankenbecler-Goldberger approximation to scattering amplitude (1962) is applied to the elastic e-H and e-He scattering. For small momentum transfers, q²<or approximately=1 (in units of a₀^-2), there is hardly any difference in d sigma /d Omega between the Glauber and the Blankenbecler-Goldberger predictions though the latter stays consistently below the Glauber prediction (1959). For larger momentum transfers, q²>>1, the difference becomes more marked with the Glauber prediction staying higher. However as d sigma /d Omega drops by three orders of magnitude at q² approximately=10 the Blankenbecler-Goldberger prediction for sigma _el will not be much different from that of the Glauber prediction.

The absolute differential cross sections of the n=2 and 3³S states of helium are obtained from threshold up to 3.6 eV above at 30 degrees , 60 degrees , 90 degrees and 120 degrees scattering angles. The energetically-dependent transmission of the post-collision analyser of the electron impact spectrometer is deduced from the known characteristics of the ionization process near threshold. The results are made absolute by normalization to accurate elastic cross sections of helium. Integral cross sections for the excitation of the 2³S and 2¹S states, and of the 2³P and 2¹P states are given at 1.6 and 2 eV above threshold, respectively.

A general expression has been derived for the coincidence intensity in (e,2e) scattering experiments at small momentum transfers. The relationship with photoelectron spectroscopy using both polarized and unpolarized radiation is discussed. The predictions of the expression have been tested using a rotatable analyser which allows measurements to be made at ejection angles of 54.7 degrees and 90 degrees . Measurements at 54.7 degrees on He, Ne and Ar verify the most significant result of the analysis, namely the existence of a magic angle at which the coincidence intensity is independent of the angular anisotropy factor beta . At an ejected angle of 90 degrees the predicted beta dependence is observed for helium. The expected independence from beta of the coincidence intensity at 90 degrees and an energy loss of 22 eV is checked by comparing branching ratios for ionization of N₂ and CO with photoelectron data.

A quantitative study is carried out of the 2p sigma -2p pi transitions which may be invoked to explain the creation of K-shell vacancies within the molecular approximation to atomic collisions. The molecular energy curves and transition matrix elements are calculated in a one-electron approximation. The theory is applied to a study of the creation of K-shell vacancies in beryllium, carbon and nitrogen and compared with the experimental results.

The straight-line semiclassical approximation is applied to calculations of K-shell Coulomb ionization of atoms by heavy charged particles, using relativistic Coulomb wavefunctions for the electrons. The effect of the Coulomb deflection of the projectile is taken into account. Numerical results both for total cross sections and for ionization probabilities as a function of the impact parameter are presented. The agreement with experiment is considerably improved for heavy target atoms. There is also an improvement over earlier PWBA calculations of the process.

Measurements of the collision damping width and shift of the sodium D lines due to noble gases are reported together with an analysis of the shape of the red wings of the D₁ line when perturbed with neon, argon, nitrogen, krypton and xenon. The results are discussed in terms of the currently available interatomic potentials and are compared with recent broadening and shift calculations.

The probability for metastability-exchange between ³He atoms in the 1¹S₀ ground state and the 2³S₁ metastable state has been measured at 4.2K using optical pumping techniques and magnetic resonance in the two hyperfine levels. The thermally averaged cross section is found to be (4.8+or-1.5)*10^-18 cm² and this result is compared with theoretical calculations.

The Anderson theory of pressure broadening of spectral lines in the microwave region (1949) is extended to permit calculations of the shifts of spectral lines. The extension is based on the analytic evaluation of double integrals. Mathematical details are presented for the dipole-dipole, dipole-quadrupole and quadrupole-quadrupole interactions. The theory is used to calculate the widths and shifts, over a temperature range from 150K to 500K, of the ammonia J=K=3-8 inversion lines perturbed by NH₃, COS and CH₃Cl, and of the self-perturbed CH₃Cl(J=0 to 1) and COS(J=1 to 2) rotational lines.

Ab initio potential curves and internuclear-distance-dependent oscillator strengths of CH⁺ are used to calculate the radiative association rate coefficient of this radical. A semiclassical treatment is developed which takes into account such collisional effects as non-adiabatic transitions between molecular states and tunnelling through the centrifugal barrier. A quantal formulation of the emission process is given, which takes into account the effect of the centrifugal potential on the vibrational nuclear wavefunctions. The value obtained for the radiative association rate coefficient cannot explain the discrepancy between the observed and theoretically deduced abundances of the interstellar CH⁺ radical.

High-resolution electron energy-loss spectra of the N₂ afterglow have revealed transitions from the first nine vibrationally-excited levels of the ground state to the b ¹ Pi _u and b' ¹ Sigma _u⁺ non-Rydberg states in the electron energy-loss range 10.5 to 12.5 eV. The results are compared with the Franck-Condon factor calculations of Nicholls (1962).