Table of contents

The classical three-body collision theory has been used to study electron-He⁺ ionization in the threshold region. The final energy and angular momentum distributions of the outgoing electrons have been calculated. The energy distribution of the two outgoing electrons appears to be in agreement with the behaviour predicted by Wannier (1953) and Rau (1971). The results also show that in the threshold region both outgoing electrons attain large angular momenta, as predicted by Fano (1975). The energy dependence of the acquired angular momentum is found to be proportional to mod E mod ^-0.5, in contradiction with the results obtained by Cvejanovic and Grujic (1975) for electron-hydrogen ionization.

The ratio of formation of doubly and triply charged ions due to L ionization of Ar has been investigated as a function of the energy loss of 8 keV projectile electrons. Rapid variations of this ratio around an average value of 10 are observed in a region of 8 eV above the L threshold. Evidence is also given for the production of Ar⁺ ions above the L threshold through ejection of a 'faster than normal' Auger electron.

Glauber cross sections for the ionization of atomic hydrogen by alpha particles and protons increase less rapidly with projectile charge Z₁ than the Z₁² dependence predicted by the Born approximation.

The differential K X-ray production probability in 420 keV Na⁺-Ne collisions as obtained from a coincidence experiment is compared with the results of a Ne⁺-Ne experiment. A possible mechanism for the observed K-shell excitation in Na⁺-Ne collisions is suggested.

Sum rule constraints have been obtained for the scattering amplitude, differential elastic scattering cross section and the total cross section for light scattering at low energies. An application of one of the sum rules is made for the case of photon scattering from the H^- ion, calculated in the asymptotic approximation.

The hook method (distortion of interferometric channel-spectra in the neighbourhood of absorption lines by anomalous dispersion) has been used to measure the gf values for Ca I, Sr I and Ba I. The gf values of lines in the principal series of Mg I, Ca I and Sr I have been plotted by the quantum-defect method to obtain a value of the photoionization cross section at the threshold. Extrapolations of the bound state gf values for Mg I, Ca I and Sr I yield cross sections at threshold of 2.36, 2.75 and 11.2 Mb respectively, all about two times larger than previous values based on vapour-pressure data.

The author points out that the Waldmann-Snider equation leads directly to quantum-mechanical expressions for the rate constants for transfer and relaxation of atomic excited state multipole moments, both in the case of resonant interaction and of foreign-gas perturbation. The rate constants are expressed in terms of quantum-mechanical partial cross sections. The effect of the hyperfine interaction is briefly discussed.

The total photon cross sections for five elements Al, Ti, Cu, Zr and Cd were measured in the energy range 15-75 keV. A modified narrow-beam geometry with a krypton filled proportional counter and an ND-512 multichannel analyser were used. The measured cross sections are compared with those of earlier investigators in the regions where the energies overlap. The photoelectric cross sections, obtained by subtracting the coherent and incoherent scattering cross sections from the total photon cross sections, are compared with the recent theoretical predictions of Scofield (1973). The experimental errors were estimated to be around 2% for all measurements.

An electron spectrometer has been constructed for the study of elastic and inelastic electron scattering processes. Up to now the apparatus has been used to measure differential cross sections of electrons elastically scattered by He, Ne, Ar and N₂. Direct absolute cross section measurements were performed on N₂ at 500 eV impact energy and at scattering angles between 5 degrees and 9 degrees . Relative cross section measurements were done on He, Ne, Ar and N₂ at impact energies between 100 and 3000 eV and scattering angles between 5 degrees and 55 degrees . The relative cross sections were put on an absolute scale by means of the apparatus calibration factor derived from the absolute measurements on N₂. Analysis of the exponential behaviour of the differential cross section as a function of momentum transfer yielded apparent polarizabilities of the target.

This paper deals with the continuation of the work described in a previous paper (He, Ne, Ar and N₂) see ibid., vol.9, no.2, p.185 (1976) and is an extension to the heavier noble gases, Kr and Xe. Relative differential cross sections for electrons elastically scattered by Kr and Xe were measured at impact energies between 100 and 3000 eV and at scattering angles between 5 and 55 degrees. The relative cross sections were put on an absolute scale by a procedure using the apparatus calibration factor derived from absolute measurement on N₂. The results are discussed in comparison with those of other authors. At the same time it was possible to derive apparent polarizabilities from the measured data.

In a recent publication Inokuti and McDowell (1974) have calculated the elastic electron-lithium cross section in the energy range up to 50 eV using a model based on a simple adiabatic 1/r⁴ polarization potential. By generalizing the model in order to take account of non-adiabatic effects it is shown that allowance for such effects is very important indeed and leads to a result consistent with the close-coupling and Glauber approximations. A careful estimate has also been made of the total cross sections for electron impact on lithium, sodium and potassium and it is found that while the normalizations of the sodium and potassium cross sections of Kasdan et al. (1971, 1973) are reasonable, the lithium cross section seems to be too large. A renormalization factor of about 0.76 is suggested for the lithium cross section.

Results obtained by quantal, semiclassical and classical theories are combined with results of experiment to obtain estimates of averaged n to n' excitation cross sections for all initial and final energy levels n and n' and for non-relativistic incident proton energies E greater than 30 keV or (100/n²) keV, whichever is the less. A semi-empirical cross section which is an analytic function of E, n, n' has estimated errors normally of the order of 20% or better.

The application of a one-electron model to describe resonant electron transfer in heavy ion-atom collisions at low velocity has been considered in detail. Simple expressions have been derived for the cross section for exchange of an electron with quantum numbers nlm. These expressions lead to a closer agreement with experiment than formulations given by Rapp and Francis (1962) and by Smirnov (1964, 1965). In particular the observed oscillatory structure in some cross sections is reproduced by the one-electron model.

For pt.I see ibid., vol.8, p.448 (1975). Direct and charge exchange processes in He⁺-Ne collisions are investigated in the energy range 250<or=E_lab<or=2000 eV using an electrostatic energy analyser for the ions and a time-of-flight spectrometer for the neutrals. Differential cross sections are measured and the collision processes are interpreted. The interpretation is based on the molecular approach to atomic collisions and employs diabatic correlation diagrams as well as calculated ab initio potential energy curves. Four different classes of collision mechanisms are required to obtain an almost complete description of the inelastic scattering.

The cross sections sigma ₂₁ at E_lab=21 keV and sigma ₁₂ at E_lab=36 keV for argon ions in argon are measured using two different production mechanisms for the incident projectile ions: direct extraction from an ion source and generation by charge exchange, respectively. It is found that long-lived metastable ions are produced by the latter method, which influence the measured cross section appreciably.

The X-ray emission of NH₃ and N₂O are reported and the main X-ray transitions are identified. A correlation between nitrogen 1s binding energies obtained by electron and X-ray emission spectroscopy is given and differences between measured X-ray energies and X-ray energies calculated from electron spectroscopy are discussed.

Ions produced by dissociative attachment in NO₂ and CO₂ are studied using a trochoidal monochromator as electron gun. Appearance potentials obtained for O^-, O₂^- and NO^- from NO₂ are respectively 1.61+or-0.05 eV, 4.03+or-0.05 eV, 3.11+or-0.05 eV. These results are, within the experimental errors in good agreement with the (D-A) values presently known. The O^-/CO₂ peak near 4.4 eV shows various structures spaced by 0.12+or-0.02 eV. These structures are connected to the vibrational structure of Co₂^- above the CO+O^- dissociation limit.

The gross spectral behaviour of the dipole oscillator strengths for absorption, ionization and dissociation of H₂, HD and D₂ has been measured over the energy range of 0 to 70 eV, using the technique of detection of forward-scattered 8 keV electrons in delayed coincidence with the ions. A quantitative collection of ionic fragments is ensured up to kinetic energies of 20 eV. The absorption results are in excellent agreement with those of Samson and Cairns (1965). By subtracting the total ionization spectrum from absorption, a region about 1 eV wide is found above the ionization potential where part of the oscillator strength goes into neutral formation. No appreciable isotope effect is observed in this region.

An algebraic scheme has been derived for the scattering properties of an arbitrary cluster of non-overlapping muffin-tin potentials surrounded as a whole by a potential shell. The modified fluster equations thus obtained determine the generalized phaseshifts and corresponding partial-wave amplitude of such a stressed cluster. The applicability of the formalism to the elastic electron scattering by molecules has been shown. As a simple example, the scattering of an electron by two fixed protons is considered.

A quantum-mechanical spectator model is applied to the scattering of atoms by heteronuclear diatomic molecules. The model allows the calculation of the energy distribution over all final rotational and vibrational states. The influence of the mass asymmetry of the molecule on this 'energy-loss spectrum' is discussed for an idealized model of the system CO+Li⁺. The probability of odd Delta j transitions, which are forbidden in the case of homonuclear molecules, is studied as a function of the mass difference of the molecular atoms.