Table of contents

It is proposed that charge exchange in Li⁺-He collisions in the keV energy range takes place mainly via rotational coupling of the ¹ Sigma and ¹ Pi states of the LiHe⁺ quasi-molecule. The potential energy curves of the ¹ Sigma , ¹ Pi and ¹ Delta states are calculated by a perturbation method for small internuclear distances. Using these curves, the differential scattering cross sections for excitation and charge transfer are calculated. Agreement with experiment is satisfactory for E theta exceeding 7 keV degree.

The least squares variational method has been used to calculate s-wave phase shifts in two scattering problems, namely the scattering of a single particle by a square well potential and the elastic scattering of electrons by hydrogen atoms.

Within the framework of the impact parameter method in the two-state approximation, it is shown that the symmetrical charge transfer cross section at a given impact velocity is inversely proportional to the ionization potential of the atom.

The authors give the contributions from the dipole and quadrupole third order interaction energy to the third virial coefficients of argon, using the m-6-8 potential function as pair potential. It is found that the dipole-dipole-dipole three-body term dominates the nonadditive effect. The results are compared with experimental data.

The authors present an experimental study of the methane excitation spectrum using the RPD and trapped electron methods. The study has shown some forbidden and allowed transitions, particularly a vibrational excitation between 1.5 and 3 eV.

By means of a theoretical approach recently developed by Pegg and Series (1970, 1973), the consequences of misalignment of the rotating field in magnetic resonance are investigated. Three main effects arise: a shift in the resonance frequency, a reduction in power broadening, and the appearance of 'multiple quantum' resonances at integral multiples of the rotating field frequency. For small misalignment angle theta , the misalignment shift is proportional to theta ⁴ and may be neglected in usual medium-precision experiments. The multiplicity of resonances should be readily detectable in optical pumping experiments.

A semi-classical approach developed by Pegg and Series (1970, 1973) is used to study higher order effects in magnetic resonance produced by an oscillating magnetic field perpendicular to a static field as the oscillating field strength is increased. It is shown that the well-known 'multiple quantum' transitions arise from a semi-classical theory, being transformed into 'single quantum' transitions induced by field harmonics in the most appropriate reference frame for treating the problem. Higher order terms in the Bloch-Siegert shift support those derived by Shirley (1965) by means of Floquet theory, and are in gross disagreement with those derived by Chang and Stehle (1971) from quantum electrodynamics, particularly at very high field intensities where the results are not even qualitatively similar. It should be possible to decide easily between the two approaches by experiment.

In calculations, to the second Born approximation, of cross sections for the scattering of electrons or protons by atoms two different Born expansions have been used. For direct processes work so far has used an expansion in terms of the final-state Green function, whereas for rearrangement collisions, the plane-wave Green function has mainly been used. In this work a comparison is made between the second Born approximations for a direct process when both approximations can be exactly evaluated-the elastic scattering of electrons or protons by hydrogen atoms in the forward direction.

Using the Schrodinger Equation as a starting point, the asymptotic form of the wavefunction is derived for a collision involving double ionization by electron impact, and expressions are obtained for the total and partial cross section. The effect of including exchange is also considered both for singlet and triplet spin states of the target atom.

For pt. I see ibid., vol.6, 259 (1973). The Born I and Born II approximations are discussed in the context of double ionization, and their behaviour at high energy compared with experiment. The Born I approximation, excluding exchange, is used to calculate total and partial cross sections for the double ionization of H^-, He and Li⁺, with various approximations used for the final state of the system, some of these being found to give good agreement with experiment.

The excitation n=1 to n=2 interval probability function for e-H collisions has been examined using a classical model. The electron-hydrogen atom long range interaction has been accounted for via a static dipole potential of the atom, and electron motion in the atomic dipole field has been examined analytically. The results obtained are used for initiations of numerical calculations in the close interaction region. A three body classical computer program by Abrines et al. (1966) has been used for the numerical calculations. The initial atomic orientation interval function per unit final energy band of the atom, for the total angular momentum L=1.665 au (plane case) has been evaluated in the energy range: 0.378<or=E (au)<or=0.411. The function obtained shows an oscillatory behaviour with two maxima at approximately 0.381 and 0.390 au. A comparison with existing experimental data and quantum mechanical results is made.

The optical potential model of Pu and Chang (1966) is extended to include EPV diagrams. Calculations are carried out for the s, p and d wave phase shifts at energies up to 17 eV. The results for s and p waves are in close agreement with those of other recent calculations and, with a phase shift analysis of experimental data. The d wave results lie between the full polarized orbital and the Green function expansion results. It is shown that third order diagrams are required for an accurate evaluation of the static polarizability, yielding alpha =1.372 a₀³, and estimates are made of the third order corrections to the d-wave phase shift, which brings the optical potential values into good agreement with the full polarized orbital results.

The photon energy dependence of the circular polarization efficiency (i.e. the ratio of the two-photon ionization probability with circularly polarized photons to that with linearly polarized photons) and the angular distribution of the ejected electrons are calculated for Li, Na and K atoms.

For pt. III see abstr. A1025 of 1971. The convergence of the pseudo-state expansion of the electron hydrogen atom system at intermediate energies is studied. The atomic 1s and 2s eigenstates as well as 3s, 4s and 5s pseudo-states are retained in the expansion and calculations in the singlet L=0 state are carried out over incident electron energies from 10.2 eV to 30.6 eV. The 1s-2s excitation cross section is found to converge rapidly, except in the region of certain non-physical resonances and this result is used to estimate the accuracy of earlier work using the pseudo-state expansion.

Simple analytic model wavefunctions consisting of two Slater-type orbitals are constructed for the 3d shells of singly ionized iron-group atoms in the 3dⁿ configuration. The parameters are optimized by a Hartree-Fock variation procedure, keeping the inner orbitals fixed. For these latter a simplified description is given, particularly suitable for the present purpose. It is shown that the values of one- and two-electron integrals associated with the 3d orbitals can be calculated to an accuracy of about 5% within the framework of these wavefunctions.

In collision of the charged particles with neutral atoms when the relative incident momentum is some ten times or more larger than the momentum of the target electron, the inelastic cross section can be expressed in terms of the incident energy and two atomic parameters, called the Bethe coefficients. In the case of the total inelastic cross section of the hydrogen-like atoms in a given initial state these coefficients in the forms of sums and integrals have been found, and for the first seven principal quantum numbers they are evaluated numerically. For these quantum numbers as the initial states a table of the Bethe coefficients for all possible excitations, ionizations and the total inelastic cross sections is given. An asymptotic formula for the total inelastic cross section for arbitrary large excited states is also given. A table published by Bethe and Salpeter (1957) for the electric dipole matrices between hydrogen-like states does not have the proper normalization. This normalization has been performed and a new table for these matrices is presented.

The He I 4026 2³P-5³D, 5³F transition has been observed in a recombination plasma at low electron densities. The profile is in very poor agreement with all existing static ion theories and the discrepancies are different in form from those for the 2P-4D transitions studied previously. New theoretical predictions are also presented showing greatly improved agreement with the experiment, and emphasizing the importance of non-adiabatic ion dynamic broadening of the forbidden component. These results cast doubt on all existing criteria for the static approximation even when frequency separations are correctly measured from the centre of the forbidden component.

The dissociative photoionization of H₂ and D₂ has been investigated experimentally and theoretically from just below threshold to 30.5 eV (405 AA). Experimentally the ratios of the number of dissociated to undissociated photoions H⁺/H₂⁺, D⁺/D₂⁺ have been determined using a mass spectrometric system essentially free from discrimination against ion species. These ratios are found to rise to plateau values of 0.0208+or-0.0017 and 0.0082+or-0.0008 respectively. Over most of the energy range investigated, the photoions are formed solely through the 1s sigma _g ionic state, permitting approximate calculations to be made. A comparison between the calculated and experimental results indicates the need for improved calculations. Significant differences are found on comparing the photoionization data reported with the corresponding values obtained by particle impact.

A model of the three-body encounters which occur in a dense gas is used to evaluate their effect on the binary diffusion coefficient of a moderately dense gas mixture. The behaviour predicted for the diffusion coefficient as a function of density is in direct opposition to that resulting from the Enskog theory of dense gases in which three-body collisions are neglected. When the entire effect of increasing gas density on the diffusion coefficient is considered an expression is obtained which leads to substantial agreement with available experimental data.

Range-energy relations have been determined experimentally for carbon tetrachloride and for several hydrocarbon liquids. Differential molecular stopping powers have hence been obtained at various energies and these are compared with values for the comparable vapour phase. The molecular stopping powers of liquid hydrocarbons are found to be lower than those of the corresponding vapours especially at low energies, and these differences are discussed.