Table of contents

A model calculation of the rates of photodetachment of negative ions shows that the usual independence of light polarization with respect to the single-photon detachment rates is appropriate only for low intensities of incident radiation. At high intensities the ratio of one-photon detachment rates (for circularly to linearly polarized light) is found to be quite generally different from unity. This is a new intensity dependent single-photon non-linear effect and should be distinguished from that associated with multiphoton transitions. It is estimated that the one-photon detachment rate in H^- by circularly polarized ruby radiation at an intensity of 3.4*10¹³ watts cm^-2 is about 21% higher than that for linear polarization of the same radiation. Other results for H^-, He^-, and Na^- using both ruby as well as neodymium lasers are also given.

For pt.III, see abstr. A7079 of 1973. The long-range nature of the Coulomb potential is taken into account in the derivation of a distorted T-matrix. When applied to elastic electron-hydrogen collisions the results are considerably better than those previously presented and compare favourably with the eikonal approximation to the second order Faddeev-Watson expansion.

High-l states of atoms, though statistically predominant, have not been studied much in the laboratory. They should, however, be excited in electron-atom collisions at energies within a fraction of 1 eV above or below the ionization threshold. This qualitative prediction derives from the Wannier theory (1953) and is, in fact, implied by Cvejanovic and Read's recent angular distribution experiment (1974). Application of the same theory below threshold provides a qualitative interpretation of a related experiment.

The ionization and dissociation of CO and H₂ by fast ³He²⁺ ions have been studied experimentally. Cross sections for secondary ion formation have been measured and interpreted in terms of predissociative and Auger processes.

K-shell vacancy sharing was measured using 200 to 500 keV Ne incident on Na, Ne, O₂ and N₂ gas targets. The experimental results are in good agreement with a previous theory assuming radial coupling between the 2p sigma and 1s sigma molecular orbitals.

A new definition of the Fermi hole in many-electron systems is provided in terms of the distribution function f^{alpha alpha} (r₁₂) of the interelectronic distance for electrons with parallel spins. By analogy with the Coulomb hole, the Fermi hole is defined as the difference between the values of f²²(r₁₂) derived from the Hartree-Fock and the Hartree wavefunctions. this definition, unlike previous ones, provides a simple picture of the Fermi hole as a function of r₁₂. By assuming that the Hartree and Hartree-Fock orbitals are identical, an analytical formula is derived for the Fermi hole. Explicit calculations are presented for the 2³S state of He and the ground state of Be. It is observed that the Fermi hole is remarkably similar in these two cases; and that the effects of Coulomb correlation are more long-ranged than those of Fermi correlation.

For pt.I, see abstr. A7075 of 1973. The coupled integro-differential equations, described in Paper I, are reduced to linear algebraic equations. The finite difference formulae used are described in detail. The linear algebraic equations are solved using a technique which has good numerical stability and which gives good linear independence in the solution vectors. The method is economic in the use of computer time and storage.

Studies have been made of the two outgoing electrons in ionization events for which the energy difference E between the total energy and the ionization energy is in the range from 0.2 to 3.0 eV. A coincidence time-of-flight technique has been used to measure their energy distribution and angular correlation functions, and a non-coincidence technique has been used to measure the partial cross section for the production of very slow electrons. The energy distribution function has been found to be uniform in the range of E from 0.2 to 0.8 eV and the width of the angular correlation function has been found to increase with the energy E in a way which is consistent with a E^1/4 dependence. The yield of very low energy electrons is consistent, in the range of E from 0.2 to 1.7 eV, with a total ionization cross section having the energy dependence Eⁿ, where n=1.131+or-0.019. These results are all consistent with the Wannier-Peterkop-Rau theory.

Using semi-empirical methods a set of analytic electron impact cross sections are developed for atomic mercury. Generalized oscillator strengths computed in the Bethe-Born approximation using an analytic independent particle model, and those obtained from experiment, are used to generate discrete excitation cross sections. Analytic expressions consistent with available data are obtained for the total and differential ionization cross sections. These results are then applied to trace the energy degradation of an incident electron in atomic mercury. Results are given for the energy loss function, eV/ion pair, and efficiencies.

The scattering of an electron with a hydrogen atom in the presence of an electromagnetic field has been considered here. A differential cross section formula has been obtained for the process in which the atom gets excited by the combined action of the electron and the electromagnetic field. Two limiting cases of the scattering amplitude have been studied explicitly: the Born approximation limit and the low frequency limit. As a byproduct of this calculation a differential cross section formula is obtained for the inverse bremsstrahlung process which contains the form factor of the atom.

The five-fold differential cross section sigma _nlm⁽⁵⁾ for ionization of the state mod nlm> is calculated for hydrogen sigma _nlm⁽⁵⁾ that the number of minima of the angular correlation in the forward direction increases with the principal quantum number. The cross sections sigma _nl⁽⁵⁾= Sigma _m sigma _nlm⁽⁵⁾ have at the direction of the momentum transfer a maximum for l=0 and a distinct minimum for l=1, besides extreme values at other angles. For neon differential cross sections of lower order and the total cross section sigma ⁽⁰⁾ have been calculated by integrating over the solid angles of both electrons and over their energy distribution. It is found that sigma ⁽⁰⁾ lies below the experimental results probably because no resonance or autoionization effects are included.

The first order Born formula is applied to elastic and inelastic collisions of potassium atoms on potassium atoms at centre of mass kinetic energies in the range 50<or=E_CM<or=100 eV. The diatomic potassium system is idealized to form an effective four body system composed of two valence electrons and two cores. It is shown that whereas this model is sufficiently flexible to fit the elastic differential cross section measurements, the excitation cross sections cannot be obtained with the same pseudopotentials. Moreover, the pseudopotentials obtained from a fit to the elastic cross sections turn out to be slightly energy dependent.

Recently four thresholds have been reported in the ionization function for the process Ba⁺+e to Ba²⁺+2e at energies of 15.8, 16.8, 19.2 and 21.9 eV. The excited Ba⁺ states involved have been identified as the 5p⁵5d(³P)6s²P_1/2 (15.8 eV), ²P_3/2(16.8 eV), 5p⁵d(³D)6s²D_3/2 (19.2 eV) and the combined 5p⁵5d(¹P)6s²P_1/2 and ²P_3/2 (21.9 eV) states. The identifications are based on Hartree-Fock calculations and intermediate-coupling calculations using scaled Hartree-Fock Parameters. The 5p⁵5d(³D)6s ²D_3/2 threshold at 19.2 eV has a finite electric dipole transition probability to the ground state due to an admixture of 5p⁵5d(³P)6s²P_3/2.

Discusses the explicit mass dependence of the charge transfer cross section for ion-atom scattering within the impact parameter approximation. For the He²⁺-H collision case the procedure of only scaling the projectile ³He²⁺ kinetic energy to facilitate comparison with a calculation based on a ⁴He²⁺ projectile without incorporating any other dependence on the mass is questioned. As an illustration of this point, it is shown explicitly in a two-state (1s,2s) calculation that for the H⁺-H and D⁺-H collisions at an impact velocity of 0.9 (au) the usual scaling procedure is not valid.

Polyatomic molecules are described by nonintegrable Hamiltonians. For such systems it has been predicted (Percival 1973) that there are two regions of the quantal spectrum with contrasting properties. Eigenvalues are obtained for the Henon-Heiles nonintegrable Hamiltonian (1964). Two regions of the quantal spectrum are found which behave differently under a slowly changing perturbation. This behaviour is required by Percival for the existence of regular and irregular spectra.

The strong coupling correspondence principle is applied to the rotational excitation of diatomic molecules by atoms. The problem is formulated for arbitrary spherically symmetric atoms and molecules in Sigma states. Various limiting cases are examined and, where possible, compared with other calculations. In particular the excitation of N₂ by Ne is considered and comparisons with close coupling calculations are made. It is shown that for wide ranges of quantum numbers and incident energies the methods used are accurate to within 10% and are faster by about two orders of magnitude. For greater initial excitation of the molecule the methods described should become more accurate.

The redistribution of vibrational energy in active nitrogen has been investigated downstream from a microwave discharge in flowing nitrogen. Changes in the vibrational energy distribution in the electronic ground state of N₂ were studied by monitoring the effect on the vibrational intensity distribution among the N₂ first positive bands emitted by a weak radio frequency discharge. It is shown that the first positive bands are produced predominantly by direct electron excitation from the electronic ground state, and that the vibrational intensity redistribution among the first positive bands therefore reflects a population redistribution among vibrational levels in the electronic ground state. The spectroscopic results indicate that the vibrational energy produced in the microwave discharge relaxes through a series of non-Boltzmann distributions as predicted by Treanor et al (1968).

An inclined beam technique has been used to obtain cross sections for the dissociative recombination of H₃⁺ with electrons for energies E between 0.38 and 4.0 eV. The ions were formed in a source which has been shown to produce H₃⁺ with negligible internal energy. The cross section is 1.03*10^-16 cm² at 1 eV and varies as E^-0.87. There is excellent accord between these results and those which Leu et al (1973) obtained at thermal energies by a microwave afterglow technique.

The collisional destruction of 5-500 keV 2s metastable hydrogen atoms in passage through H₂, He, Ar, Kr and N₂ has been investigated using a modulated beam technique. Cross sections sigma _2s.1 for one-electron loss and total cross sections sigma _D for all collisional destruction processes have been separately determined. Electron capture leading to negative ion formation is found to be relatively unlikely at the highest energies considered sigma _2s.1 approximately= sigma _D. Cross sections for de-excitation sigma _2s.1s approximately=( sigma _D- sigma _2s.1) increase in relative importance with decreasing impact energy. Values of both sigma _2s.1s and sigma _D for H₂ and He agree with estimates based on the first Born approximation. The growth and equilibration of H(2s) atoms in electron capture by protons in H₂, He, Ar and N₂ has also been investigated and interpreted quantitatively in terms of the relevant collision mechanisms.

Valence configuration interaction (VCI) and self-consistent (SCF) calculations, using a common basis set for each model, are compared for diatomic oxygen and sulphur. Potential energy curves and spectroscopic constants are presented for the ground states of both systems and comparisons are made with experiment. For sulphur, energy calculations are carried out for the ³P atomic state and the a¹ Delta _g and b¹ Sigma _g⁺ excited states of S₂.

Ab initio Hartree-Fock calculations have been performed on some low-lying electronic states of AlF. Results clarify the problem of character and configuration of some observed states, to which the rather large amount of spectroscopic data presently available cannot provide an answer. An explanation has also been given for the fact that states of the pi ³ pi configuration have been observed for CO and N₂ but not for AlF although these molecules have similar electronic structures.