Table of contents

Using an electron transmission spectrometer the additional core-excited resonances in the total cross section for scattering of electrons by molecular hydrogen in the energy range 11.0-13.0 eV are located. The energies of these additional resonances are in good agreement with those recently measured by Joyez et al. (1973) in an inelastic channel.

It is shown that the oscillator strengths for several transitions in He are more accurate in the MCHF than the HF approximation and that this improvement cannot be attributed to the charge distribution function. The important configurations are those which contribute significantly to the state under consideration and at the same time, have an allowed transition to the dominant configuration of the other state. Thus all external correlation may be important in the accurate determination of oscillator strengths.

A previous calculation (Taylor and Thomas 1972) suggested the existence of a second resonant state of H^2- which has since been observed experimentally at 17.2 eV. A new analysis of the calculated data yields a state which is 60 per cent (2p)³ and 20 per cent (2s)²(2p) with an energy of 17.26 eV.

The excitation of the first excited levels of krypton with the configuration (4p⁵5s) by electron impact has been observed near threshold. The experiment was carried out in a crossed-beam arrangement, using an electron monochromator of the 127 degrees type with an energy width of less than 100 meV. The ultraviolet photons were observed at 90 degrees with respect to the beams. The excitation function near threshold is dominated by a strong resonance and comparison is made with experiments on the inelastic scattering of electrons from krypton.

Calculations for the Stark broadening of H alpha and H beta using a unified theory for both ions and electrons are presented in the density range 10¹⁴ to 10¹⁵ cm^-3 at a temperature of 10⁴ K. Although the theory is of marginal validity at these densities, it shows quite conclusively the influence of ion dynamics in reducing the dip at the centre of the H beta profile and the peak in the centre of the H alpha profile.

Vanadium XVI to XXI emission lines are classified in spectra radiated from a laser produced plasma. They provide additional confirmation to the identification of isoelectronic Fe XX to Fe XXIV lines which are emitted from solar flares.

It is shown, both qualitatively and quantitatively, that the n dependence of the singlet-triplet splitting of the singly excited HeI-like spectra follows the theoretical law Sigma _{nu =0}^l a nu (l,Z)/n^{2 nu +3} in contrast to the n^-2 dependence suggested empirically by Elden and Lofstrand (1970).

Ar-L X-ray production cross sections for collisions of He⁺, Ne⁺ and Ar⁺ ions of energies between 100 keV and 1 MeV with Ar atoms have been measured. The results are in good agreement with comparable cross section data.

Significant discrepancies between Ar L-shell fluorescence yields as determined from total cross sections and from spectral measurements in Ar-Ar collisions are shown not to be due to an error in the measured X-ray cross sections, as was suggested by Fortner and Garcia (1973). Discrepancies originate from ambiguities in identifying the atomic states involved in their spectral method.

A triple centre approximation is proposed to describe proton-hydrogen charge changing collisions. Favourable agreement with experiment encourages further research into the applicability of three centre expansions.

Cross sections sigma _11* for the formation of He⁺ (2S) metastable ions by excitation of 10-40 keV He⁺ ions in passage through He, Ar, Kr, H₂, N₂ and O₂ have been determined. These cross sections are strongly energy dependent but are at least two orders of magnitude smaller than corresponding cross sections sigma _21* for He⁺ (2S) formation in electron capture by He²⁺ ions.

Relative electron impact ionization cross sections for the metastable 2³S and 2¹S states and for the highly-excited, long-lived states of helium were obtained using a double electron beam technique.

The consistency of recent measurements of total cross sections for positrons in helium is examined using forward dispersion relations.

Excitation of the ground state vibrational modes of CO₂ has been studied in an electron impact experiment in the energy range 3-5 eV. A series of oscillations is observed in the excitation functions of the elastic and vibrational channels which was previously assumed to result from vibrational excitation of an intermediate negative ion (shape resonance). The oscillations were seen to move towards higher energies with increasing vibrational quantum number when observed in the symmetric stretch channel. This leads us to propose that the structure is due to an interference effect in the negative ion wavefunction (boomerang model).

The potential scattering of electrons in the presence of an EM field has been formulated by taking the approach of the Glauber approximation. An expression for scattering amplitude is obtained which in the high energy limit reduces to the known Born approximation result. The low frequency limit of the scattering amplitude has also been given.

Radical profiles of the emission from upper laser levels in a helium-selenium discharge have been obtained and a central dip is apparent for discharges operating in lasing conditions. A model to explain the effect is proposed.

The excitation transitions considered are 1¹S to 2¹P and 1¹S to 3¹P. Electron correlation is introduced into the description of the 1¹S ground state in a systematic way by using the natural expansion of a configuration-interaction (CI) wavefunction developed by Weiss. By truncating this expansion to the first X terms and renormalizing a series of wavefunctions ranging from a Hartree-Fock equivalent (X=1) to the full CI function (X=15) are obtained. Operating within the first Born approximation, three standard formulations for evaluating f(K) are used and their sensitivity with respect to correlation effects is discussed and a comparison of the present results is made with those of other workers. Although the inclusion of the first correlation configuration in the 1¹S wavefunction did not necessarily guarantee an improvement in f(K), the introduction of the second correlation term in the natural expansion gave rise to a significant improvement in f(K) for all K regardless of the mode of calculation.

Free ion relativistic Hartree-Fock results have been used to calculate energies and chemical shifts of K and L X-rays in Mo, Sn and some rare earths. Agreement with experimental chemical shifts in Sm and Eu is good. When exchange is treated fully, the relative magnitude of the K_{beta 1} and K_{beta 3} shifts between di- and tri-valent rare earth ions is shown to depend strongly on whether the electron involved in the change of valence state is from the 4f- or 4f+ group. Further experimental checks on this prediction are suggested. The method is compared with Mossbauer isomer shifts as a means of deducing the electron configuration of crystal chemical bonds.

The effect of the nuclear charge on any given orbital electron is reduced by the screening effect of the other electrons in the atom. Values of sigma ₂, the Sommerfeld constant which is a measure of this screening, can be obtained from the difference between energy levels belonging to a spin doublet. New values of sigma ₂(Z), with probable errors, have been calculated for the L₂L₃, M₂M₃, M₄M₅, N₂N₃, N₄N₅, N₆,N₇, O₂O₂, and O₄O₅ doublets over the entire range of atomic numbers. Z. The method used is shown to be superior to the usually employed Sommerfeld's approximation. A study of sigma ₂ against Z yields several interesting conclusions, the most important one being that the best calculated values for the binding energies of electrons in the transuranium elements give too large a separation between the members of the L shell spin doublet. Several anomalous energy level spacings are pointed out and new values for the L shell spin doublet separation for the transuranium elements are given.

The electron-2¹P helium differential cross section is calculated using the Glauber theory for several energies. The results are compared with the recent experimental data of Opan and Beaty (1972), the extensive first Born calculations of Truhlar et al. (1970), and the coulomb projected Born calculations of Hildago and Geltman (1972). Also, the total cross section is calculated and the results compared with the experimental results of Jobe and St John (1967). In general, the results for 2¹P helium show the same improvement as Tai et al. (1970) demonstrated for the hydrogen differential cross sections.

The cusp in the cross section for the elastic scattering of electrons by helium atoms at the energy of the 2³S threshold has been measured at scattering angles from 25 degrees to 100 degrees . High resolution measurements at 90 degrees have shown that the s wave phase shift is 107 degrees +or-11 degrees at this energy. The energy of the 2²S resonance has been accurately calibrated from the position of the cusp and it has been found to be at 19.367+or-0.009 eV, with a natural width of 9+or-1 meV. The s wave phase shift at the resonance energy has been found to be 106 degrees +or-3 degrees . The 2¹S cusp has also been studied.

The derivative of the electron transmission spectrum of helium has been directly measured for electron energies between about 19.2 and 21.2 eV. Effective range theory has been used to extrapolate the 2²S state of He^- across the 2³S threshold of He. Such extrapolation produces a peak in the energy derivative of the transmitted current at the 2³S threshold which was used to calibrate the electron energy scale. This calibration technique has been used to identify the positions of the other n=2 thresholds. The position of the dip in the elastic cross section due to the 2²S state of He^- is thus established at 19.35+or-0.02 eV. Two additional structures have been observed between (He^- (2²S)) and (He (2³S)) and three between (He (2³S)) and (He (2¹S)) in agreement with the results of Golden and Zecca (1970). Several additional features in the spectrum are also discussed.

A new gauge condition which leads directly to the 'multipole' hamiltonian for the interaction of molecules with the electromagnetic field is studied within the context of quantum electrodynamics ie when the molecules and field are considered as a closed dynamical system. The new formalism which maintains the advantages of the usual Coulomb gauge theory but avoids the difficulties associated with the presence of unphysical terms in the propagation function of the Coulomb gauge vector potential, is thus obtained without recourse to the unitary transformation of the usual Coulomb gauge formalism which has previously been used to achieve this result.

Approximate Hartree-Fock wavefunctions are obtained for the ground and low-lying states of TiH, whose internuclear separations and vibrational frequencies are predicted. Correlation energy differences are estimated from atomic data, and the relative energies of low-lying states predicted. The ground state is calculated to be ⁴ Phi . The dissociation energy of the molecule is predicted to be approximately 1.6 eV.

A vibrational analysis of three band systems of the AgBi molecule is reported. The indigo, red and infra red systems, lie respectively in the 4700-4950 AA, 6000-6400 AA and 8000-8300 AA ranges. These red-degraded band systems show no usable resolved rotational structure. Nevertheless the existence of extra-heads and inflexion peaks in the red and infra red systems allows the determination of approximate values of certain rotational constants. These values are improved by a minimization procedure using a computer.

Experimental results are presented on cluster ions sputtered by primary ion bombardment from some CuBe and CuAl alloys. Emission intensities of these aggregates present alternations according to the parity of the number of Cu atoms: Cu_nBe_m cluster ions behave as Cu_n⁺ ions with enhancement of n odd numbered ions; Cu_nAl_p cluster ions are found to be favoured when n+p is odd. These intensity maxima and minima are related to the external electronic structure and an attempt is made to explain this peculiar behaviour from the Huckel model.

The mobility of potassium ions in the gases helium, neon, and argon has been measured at respective gas temperatures of 303, 302 and 304 K with an estimated accuracy of 1%. From the variation of the mobilities with E/N, the ratio of electric field strength to gas number density, the ion atom interaction potentials have been derived. This derivation makes use of the mobility theory of Kihara (1953) as presented by Mason and Schamp (1958) which is found to be capable of accurately predicting the mobility at low and intermediate electric field strengths.