Table of contents

Total cross sections for the 1s-2p excitation of atomic hydrogen by electron impact, calculated in the Glauber approximation, are compared with the predictions of the various forms of the Vainshtein approximation.

A trapped electron experiment is used to observe resonance phenomena in the electron impact excitation of helium. For precise collision chamber conditions, very sharp and complex structure is observed which correlates well with the known series of resonances in the 19.8-22 eV energy range.

In solving the relativistic scattering problem by the method of Sommerfeld and Maue (suitably iterated Dirac equation, expansion in powers of Z/137) one usually first obtains an approximate scattering wavefunction in coordinate space, from which the scattering amplitude is then extracted. An alternative method is presented here, based on the Sommerfeld-Maue Hamiltonian, but working in momentum space and aimed directly at the T-matrix. To the first order in the expansion parameter it yields simple formulae which should prove useful for numerical computations.

The interaction of an atom with two radiofrequency fields is examined theoretically by considering the dressed atom. The effect of rf fields on the resonances is treated exactly. Results are obtained for a two level system with applied sigma and pi fields.

The application of a generalized impact parameter treatment to proton-hydrogen atom scattering is described. In this model the motions of the particles are not considered to linear trajectories with constant velocities as in existing treatments of the problem. The results of these calculations are in good agreement with experiment and are shown to be considerably better than comparable calculations using the linear-trajectory, constant-velocity model.

Reports the measurement of energy and angular distributions of electrons ejected from helium by 100 eV to 2000 eV electrons. The results are integrated over angle to give secondary electron energy distributions which are compared with recent Born approximation calculations. The Born exchange approximation represents the 100 eV data surprisingly well.

The He⁺-He collision is investigated using a molecular expansion which takes account of rotational coupling between the ² sigma _u and ² Pi _u states and between the ² Sigma _g, ² Pi _g and ² Delta _g states of the He₂⁺ quasimolecule. Differential cross sections for elastic scattering, resonant charge transfer, direct and exchange excitation of He(1s, 2p) ^1,3P, He⁺(2p) and of the autoionizing state He(2p²) ¹S, ¹D have been computed for a range of energies from 300 eV to 1.5 keV and for a range of scattering angles from 0 to 24 degrees (in centre of mass system). The agreement with experiment is satisfactory. For E theta >or approximately=3 keV deg, it is seen that rotational coupling is the dominant mechanism for the excitation of inelastic transitions. The consequences on the determination of potential energy curves from scattering data are briefly discussed.

A 'quasi-diabatic' representation based on LCAO-MO-SCF electronic wavefunctions, satisfying to a large extent Lichten's original suggestion and Smith's theoretical definition for diabatic states, is introduced. Potential energy curves of the HeNe⁺ molecular ion have been obtained in this framework and subsequently used in computing differential cross sections for the inelastic scattering of He⁺ by Ne in the Landau-Zener two states approximation. The shape and the location of the crossings of the potential energy curves agree with the experimental predictions of Coffey et al. and Baudon et al. The transition matrix element at the outer crossing is calculated as an electrostatic interaction term and the value obtained is 0.26 eV. Some arguments are presented which suggest that the experimental values are overestimated.

Studies have been made of resonant scattering of electrons from N₂ in the energy region 11 eV to 13 eV. By measuring cross sections for scattering leaving the target molecule in vibrational levels of the ground state the potential curve of a state of N₂^- has been determined. The symmetry of this state appears to be ² Sigma _g⁺ and an estimate has been obtained of its width. Additional structure has been observed in the elastic channel and this is discussed.

The electron-phonon coincidence technique was applied to the measurement of lifetimes in N₂ and H₂. In this method the inelastically scattered electrons are analysed and used to select the upper state of interest, thus eliminating the systematic errors due to cascading and the spectral overlap of different band systems. The lifetimes of the first three vibrational levels of the C³ Pi _u state of N₂ were found to be 35.6+or-0.5, 34.9+or-1.8 and 34.5+or-2.3 ns, and those of the first two vibrational levels of the a ³ Sigma _g⁺ state of H₂ were found to be 11.0+or-0.42 and 10.6+or-0.6 ns.

Lifetimes of Ov levels have been measured by the beam-foil technique, transition probabilities and oscillator strength have been deduced and compared with values computed in the Bates and Damgaard approximation.

A method is devised for estimating the perturbation on the vibrational states of a molecular ground electronic state due to the presence of a polarizing charged particle. The adiabatic polarization potential for the H₂⁺-e^- system is expanded about the equilibrium internuclear distance, R_e, and the linear term is treated as a perturbation on the harmonic oscillator states of H₂⁺. The perturbation problem is solved exactly, and the 'shifted' oscillator states are shown to yield a reduction factor of the form exp(-E_JT/2 omega ) when their overlap with an unperturbed oscillator state is evaluated, and E_JT is defined as the Jahn-Teller energy, proportional at large scattering electron distances to the square of the derivative of the H₂⁺ polarizability at R_e divided by the eighth power of the electron distance. At intermediate distances E_JT can be a significant portion of the vibrational spacing omega .

Many-body theory in diagram form is applied to atomic closed shells in order to analyse the role of many electron effects in atomic photoabsorption spectra. Interest is focused on the random phase approximation expansion. It is shown that the coupling matrix elements have to be treated in an exact way making impossible the infinite summation of the series. However, the photoabsorption cross section is proportional to the spectral function (imaginary part of the polarizability). The spectral function is then expanded in perturbation series. The series can be partially summed to infinite order to give the spectral function as a ratio of expansions representing a screened external and a screened internal interaction. The theory is applied to helium to show that many-body correlations of RPA type are very important when calculating the corrections to Hartree-Fock type one-electron spectrum.

Franck-Condon factors and related quantities have been calculated for the Fox-Duffendack-Barker and ultraviolet doublet systems of CO₂⁺ which are important contributors to the dayglow from the Martian atmosphere.

A relationship between spin-spin and derivatives of electron repulsion integrals, noted by Schrader, is extended and applied to obtain a simple analytical formula for two-centre Coulomb, spin-spin integrals over Slater orbitals. The method is also illustrated by deriving the Gaussian transform expression for a four-centre, spin-spin integral.

Lower bounds to the energy levels of the ground states of the helium isoelectronic sequence and of excited singlet and triplet S states of He and Li⁺ have been calculated, using analytical orbital wavefunction of 'frozen core' type and a variety of lower bound formulae. Only the bounds which result from the formulae of Cohen and Feldmann are generally useful. The numerical results indicate that the 'frozen core' wavefunctions for two-electron atoms are of satisfactory quality.

Gives lithium, beryllium, boron and carbon-like spectral line classifications of F III to VII, Na VI, Na X, Mg VII, Mg X, Al VIII, X, XI, and Si IX and XII which are based on observations of laser produced plasmas. The identifications are mainly of transitions between levels of principle quantum number n=3 and 4 but also include 2s2p³-2p⁴ transition singlets in the carbon isoelectronic sequence. The lithium-like 3p 2P-4d ²D classifications can be applied to intensity calibration of the spectral region between 120 and 200 AA.

The theory of quasi-stationary states given by Hayasi and Lee for some L_alpha satellites such as alpha ₂', alpha ₃, alpha ₄, alpha ₅, alpha ₅', alpha ₆, alpha ₇ and alpha ₈ of metallic silver is examined in the light of the new assignment of the parent line of these satellites. A fresh correlation of these satellites with corresponding absorption maxima is shown and discussed together with the correlation put forward earlier by Hayasi and Lee. The theory is found to be adequate to explain the emission of these satellites.