Table of contents

Differential cross section measurements of the ionization of metastable He* atoms in collisions with ground state He have been performed in the energy range E=50-199 eV. The most prominent peak in the energy loss distributions of the product ions occurs near the ionization threshold ( Delta E approximately=5eV), implying the ejection of very low energy electrons. The angular distribution of this prominent feature is very strongly peaked at 0 degrees , displaying no apparent angular threshold, and its intensity increases substantially with increasing collision energy. This behaviour is consistent with a mechanism in which a small fraction of the incident flux follows the diabetic ³ Sigma _g⁺ potential of He(2³S)+He. Ionization occurs as this state crosses the continuum state He₂⁺(² Sigma _u)+e, near the bottom of its potential well.

The resonance lines of the third spectrum of each of yttrium and lanthanum have been observed in the emission from a cold helium afterglow plasma when a small concentration of the element is introduced. The excitation is attributed to formation of the ions in the upper levels directly, as a result of hybrid charge-transfer/Penning reactions with He⁺ ions.

The amount of multiple L-shell ionization is studied as a function of the ionic charge of the projectile. This is done by measuring the relative intensities of the K alpha satellite lines in neon. It is found that the multiple ionization produced by projectiles having the same ionic charge is similar when only K-shell electrons are bound to the projectile. This suggests that the K-shell electrons screen the nuclear charge during the ionizing collision.

Theoretical calculations and experimental measurements are presented for the static polarizability of some argon ions. Using a modification of the method of Sternheimer (1969) for the calculation the values alpha _Arn=7.4a₀³, alpha _ArIII=5.3 a₀³ and alpha _ArIV=3.9 a₀³ were obtained. The value for Ar II agrees with the experimental result alpha _ArII=7.2+or-0.4 a₀³ deduced from the report of Bristow and Glass (1972). Recent experiments in the double diaphragm free piston shock tube (Sandeman and Allen 1971) produced first and second ionized argon plasmas behind incident normal shock waves. Analysing the results of time resolved interferometry in these experiments gave the result alpha _ArIII=7a₀³. This analysis required a calculation of the plasma composition behind normal shocks into argon (considering ions up to Ar IV and assuming local thermodynamic equilibrium) and a theoretical study of the optical dispersion of the plasma.

Multi configuration Hartree-Fock (MCHF) wavefunctions of barium were used for a configuration interaction calculation including spin-orbit coupling. Since the energy spectrum of the interacting states is rather dense the mixing parameters of the intermediate coupling wavefunctions show unexpected high values as a consequence of resonance in energy. For this effect indirect interaction is important. Even though the calculation can't predict correct amplitudes in those cases the effect must be real. Its bearing on transition probabilities was studied.

Ab initio molecular orbital calculations on low-lying states of TiH and VH are presented; these suggest that states not considered in a previous study of TiH may be low-lying. Configuration interaction is performed between near-degenerate states, and it is concluded that the H atom acts only as a small perturbation on the Ti and V atoms. The ground state of VH is predicted to be ⁵ Delta .

The rotational excitation of N₂⁺B² Sigma _u⁺ formed in collisions of 20 keV with N₂ is shown to be adequately characterized by a Boltzmann distribution having a rotational temperature equal to the kinetic temperature of the nitrogen target.

The experimental results of Crowe and McConkey (1973) on the dissociative ionization of H₂ by electron impact are compared with theoretical calculations on the autoionizing states of H₂. The structure of their proton production spectra can be interpreted as evidence for the existence of four autoionizing states Calculated cross sections agree semiquantitatively with experiment. Cross sections for the ejection of electrons by electron impact and photoionization have also been calculated.

A comparative study is made of several lower-bound procedures for calculating the eigenvalues of a simple exactly soluble one-dimensional potential, when this potential V(x) is regarded as the sum of two harmonic-oscillator potentials ¹/₂(R-x)² and ¹/₂(R+x)² centred at x=+or-R. This potential resembles a molecular potential, the wavefunctions for which are to be represented as combinations of the 'atomic' wavefunctions of the two separate potentials ¹/₂(R+or-x)². The resulting LCAO-type wavefunctions are chosen to give lower bounds according to the classical methods of Weinstein and Stevenson (1938) and the truncated hamiltonian method of Bazley and Fox (1963); upper bounds are also obtained according to the Rayleigh-Ritz principle. The calculations are made for different values of R. Acceptable energies can be calculated by all methods. Of the methods considered the Rayleigh-Ritz upper-bound method converges most rapidly; the Stevenson lower bound is best if the optimum value of a certain parameter is known; the Weinstein method gives the poorest convergence of all.

Derives the equations of motion for the density matrix of a two-level molecule interacting with two oppositely propagating semiclassical waves. The equations are shown to correctly reproduce earlier results by Kol'chenko et al. (1969) for one travelling wave, and their perturbation treatment for a standing wave. The saturated absorber experiment is treated in the case when one travelling wave is weak enough to allow a perturbation expansion in its amplitude. The velocity dependent absorption function is investigated in detail, and the effect of recoil on the processes: Raman scattering, Rayleigh scattering and dynamic Stark splitting is obtained and discussed. These have been treated without recoil by Haroche and Hartmann (1972) and a detailed comparison with their work is included. Finally there is a brief discussion of the importance of recoil for different situations in quantum electronics.

The energy dependence of the yield of Auger electrons for different electron primary energies are examined for N_6,7O_4,5O_4,5 transitions in Au, Bi and Pb. Apparent thresholds are observed at around 60-70 eV greater than those expected from X-ray photoemission spectroscopy. The anomalous ionization profile cannot be explained by cascade from deeper levels, but a mechanism analogous to the process of 'delayed transitions' in the X-ray absorption of 4f levels is suggested.

The high resolution M_4,5N_4,5N_4,5 and M_4,5N_4,5O₁ spectra from cadmium vapour have been measured using electron impact excitation. The fine structures of the spectra, not earlier observed in the measurements from solid cadmium targets, have been interpreted by comparison with calculated line energies and intensities. The calculations have been made applying intermediate coupling with configuration interaction to the final states. Good agreement between the calculated and experimental results has been found. For the M₄ and M₅ levels of the free cadmium atom the following widths and binding energies have been obtained: Gamma (M₄)= Gamma (M₅)=0.35+or-0.05 eV, E(M₄)=418.7+or-0.5 eV; E(M₅)=411.9+or-0.5 eV.

Several states of neutral Ba were calculated in the non-relativistic multi-configuration Hartree Fock approximation. Energies and mixing parameters were found. Oscillator strengths for dipole transitions are given and compared with values in the literature. The transition probability of the infrared line 6¹P⁰-5¹D at 15000 AA is negligible compared to that of the resonance line 6¹P⁰-6¹S. The quadrupole transition probability of 5¹D-6¹S at 8775 AA is about 2 s^-1.

Using a level-crossing technique lifetimes of states in the 3d⁹4s4p(³P) configuration of the Cu I spectrum have been determined. From this data and previous measured lifetimes of the 3d¹⁰4p²P_3/2⁰ and 3d⁹4s4p(³P)⁴P_3/2⁰ states absolute oscillator strengths are deduced, taking into account small corrections, involving the decays to the metastable 3d⁹4s²²D_5/2,3/2states. Taking these values in combination with other absolute oscillator strengths derived from relative oscillator strengths measured by the anomalous dispersion and absorption method, altogether oscillator strengths for nine transitions measured by different methods are used to evaluate two one-electron radial dipole matrix elements for the transitions 4s-4p and 3d-4p by an optimized fit using eigenfunctions calculated from fine structure energies.

The significance of the operator: V'=g beta /2mc² Sigma _is_i*p_i.E which arises in the molecular relativistic Pauli Hamiltonian is investigated in relation to the Stark effect of the hydrogen atom, degenerate diatomics and symmetric top molecules. For the hydrogen atom under low-field conditions V' decreases the splitting linear in the field but the effect is not thought to be observable at present. V' does not affect the linear Stark effect of molecular systems in the absence of electronic-rotational coupling.

The time-dependent Hartree-Fock method (or random phase approximation) has been used to derive a coupled system of integrodifferential equations which can be used to calculate excited state-excited transition densities. The physical interpretation of these equations is also given.

Results are presented for the photoionization of the (3s, 3p:¹P) state of magnesium, for ejected electron energies in the range 0.06 to 0.245 Ryd. Dipole length and velocity matrix elements were calculated using a configuration interaction initial state wavefunction and a close-coupling final state wavefunction. The broad features of the cross section are due to transitions to ¹D states, with the ¹S transitions appearing as sharp peaks on the ¹D background. A (3p, 4p:¹D) autoionizing state was identified at 0.205 Ryd with a width of 0.03 Ryd.

The population of the potassium fine structure states 4²P_1/2 and 4²P_3/2 has been determined from the emission intensity of the fine structure components K(4²P_1/2 to 4²S_1/2) and K(4²P_3/2 to 4²S_1/2) after excitation in collisions with Hg, N₂, O₂, CO₂ and NO₂. The energy dependence of the population ratio is investigated for the above species in the energy range between 2 and 50 eV.

For pt. I, see abstr. A13527 of 1974. The X-ray emission spectrum of an ion having an inner-shell vacancy moving through a solid is discussed using Weisskopf's theory of collision broadening (1933). In particular the approximations involved in a previous treatment which used the 'static' approximation are clarified. The analysis of the problem is illustrated by a direct evaluation of the emission spectrum of a model system by means of a numerical Fourier transform. The calculation demonstrates that the simpler static approximation is adequate except near the classical cut-off frequency where the dynamic variation of the molecular orbitals causes a broadening beyond this cut-off frequency. An estimate of this broadening is given.

A model is proposed to describe a collision between an electron and a polar molecule and calculations of the rotational excitation of the alkali halides CsF, CsCl and KI are presented. It is shown that the predicted momentum transfer cross sections are much smaller than those obtained by using Born's approximation, and that the differential cross sections differ both in magnitude and shape at large scattering angles. A scaling procedure is presented which facilitates the evaluation of rotational excitation cross sections.

Absolute cross sections for single-electron capture and single- and multiple-electron loss by 100- to 500-keV oxygen atoms and ions in collision with H₂ gas molecules have been measured. The charge-state distribution of the fast beam emerging from the target cell was measured by electrostatic separation of the various components and subsequent counting by a secondary-emission, position- sensitive detector. Cross sections were determined from non-equilibrium charge-state distributions by a least-squares technique.

A study is made of the excitation of atomic hydrogen to the 2s, 2p, 3s, 3p and 3d states by collision with helium and of excitation of the 2 ¹S and 2 ¹P states of helium by collision with atomic hydrogen. The first Born approximation is employed to calculate total cross sections (with full account taken of double transitions) for 3s, 3p and 3d excitation and to calculate the polarization of Lyman alpha radiation emitted from H(2p). The effect of coupling of states is investigated for single transition reactions (the target atom remaining in its ground state) occurring in all the above excitations by employing the impact parameter method and including ten states.

Differential cross sections are presented in the Born, unitarized Born, two- and four-state treatments of the elastic and the 2s and 2p inelastic scattering of H1s) by the He⁺(1s), with impact speeds nu _i in the range 0.5<or= nu _i<or=3 au. For elastic collisions, the Born approximation is successful only for large-angle scattering while for inelastic scattering it fails completely for large angles at all nu _i, and for small angles at low nu _i, when the effects of couplings to other close channels are important. Corresponding treatments are also carried out for H⁺-H(1s) collisions, which represent the behaviour of He⁺(1s)-H(1s) collisions in the limit of high-impact-energies when the valence electron in He⁺(1s) completely screens its parent nucleus.

Differential measurements are reported on elastic charge exchange and direct excitations for H⁺ on H between 250 eV and 2000 eV, using the energy loss method. Evidence is found for the exclusive excitation of n=2 levels. Charge exchange probabilities are in good agreement with the previous data of Everhart (1965) and improve them at low energies and angles. Experimental cross sections for all process are compared with the available theoretical data in the molecular expansion revealing the effect of 'trajectory' calculations for large angles.

The first-order distortion method is used to calculate the cross section for proton impact excitation of neon to levels of the 2p⁵3s and 2p⁵3p configurations. The results are compared with the proton energy loss measurements of York et al. (1972). The distortion method shows considerable improvement over the first Born cross sections in the energy range up to 200 keV. A solution of the coupled equations for the scattering problem within a set of initially degenerate sub-states gives a negligible improvement of the distortion result for the total cross section.

A widely occurring error in the evaluation of the closure term in the simplified second Born approximation to electron- helium scattering is corrected. The corrected theory is applied to the elastic scattering of electrons and positrons by the 1 ¹S ground state of helium in the energy range 50 eV to 800 eV. The full second Born approximation, in which cross sections are calculated by squaring the modulus of the full second Born amplitude, and the third-order second Born approximation, in which the second Born cross section is only evaluated correct to third order in the interaction potential, are both shown to be poor. A modification of the second Born approximation first used in the original work of Massey and Mohr (1934) is adopted. This 'new' approximation gives special treatment to the coupling of the 1¹S state to itself. The results obtained are in much better agreement with experiment. Exchange effects are also taken into account in electron-helium scattering and appear to be important up to quite high energies. Positron-helium differential cross sections are found to be smaller and flatter than the corresponding electron cross sections.

Generalized Boltzmann and Saha formulae for populations of atomic levels and degree of ionization for a two-temperature plasma in non-thermal equilibrium are given. Inelastic atom-atom type collisions are taken into account. Calculations based on these formulae are performed for optically thin or Lyman series optically thick hydrogen plasmas. They are in good agreement with results obtained by solving the non-linear set of balance equations numerically. In some cases atom-atom collisions change the results by a few orders of magnitude. The radiative source function of the strongly non-LTE and optically thin plasma is determined. It coincides with the Planck distribution for a wide frequency band.

Valence Configuration Interaction (vci) wavefunctions have been used to obtain potential energy curves for several states of the F₂⁺ and F₂⁺⁺ molecular-ions. Where applicable, spectroscopic constants and transition wavenumbers have been determined and compared with experiment.