Table of contents

Cross sections for electron impact ionization of krypton due to ejection of a 3d-shell electron have been calculated using screened hydrogenic and Hartree-Slater wave-functions for the target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3d electrons, are widely different in the two approximations. The angular distribution due to the Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

The probabilities of K-vacancy sharing in heavy-ion-atom collisions have been calculated by applying the two-state exponential model of Nikitin (1962, 1970) to the 1s sigma -2p sigma radial coupling. The agreement with experiment is satisfactory. The results suggest an explanation of the discrepancies between the Meyerhof formula and the K-vacancy-sharing probabilities for light collision systems (Z_H+Z_L<15).

Two band systems have previously been observed and attributed to the SiCl₂ radical by Asundi et al (1938). These bands are shown to be due to three well known systems of the PO and P₂ radicals.

K, L and M resonance and inner-shell X-ray line spectra have been recorded from high-energy-density exploded-wire plasmas for elements throughout the periodic table. Analysis of the resonance spectra shows that the following ionization stages were attained in dense pinches in the plasmas: He-like Cu²⁷⁺, Ni-like Ag³⁷⁺ and Ni-like Au⁵¹⁺. Using a coronal model to describe the plasmas results in estimates of the electron temperatures of approximately 1 to 2 keV. The inner-shell spectra were produced by a non-thermal high-energy component of the electron distribution.

A dressed-atom approach to resonance fluorescence in intense laser fields is presented. Simple and general results are derived which include the now well known predictions concerning two-level atoms but are not restricted to such simple cases. The positions of the various components of the fluorescence and absorption spectra are given by the allowed Bohr frequencies of the total system: atom+laser mode (dressed atom). The master equation, describing spontaneous emission from the dressed atom is solved in the limit of high intensities. Simple expressions, taking into account the effect of cascades, are derived for the widths of the components.

The general method developed in a previous paper (see ibid., vol.10, p.345 (1977)) is applied to the problem of resonance Raman scattering in very intense laser fields. At very low intensities the spectrum consists of three monochromatic lines (Rayleigh, Raman Stokes and anti-Stokes) which split into a triplet and two doublets when the laser light, tuned on one of the two transitions connecting the upper state to the two lower sublevels, has a sufficiently high intensity to saturate this transition but not the second one. The Raman and Rayleigh lines are completely mixed when the intensity becomes so high that both transitions are saturated. The corresponding evolution of the spectrum is determined. Optical-pumping effects leading to asymmetries in the fluorescence spectrum are taken into account.

A correct asymptotic behaviour is imposed on the Dalgarno-Kingston and the Bell interpolation formulae for the sum-rule function S(k). Extrapolation procedures then give S(-4), S(-6) and S(-8) and subsequently van der Waals constants from (2,1) Pade approximants. The investigations are made within empirical as well as the CHF schemes.

The power series of the lowest eigenvalue epsilon ( lambda ) of the helium isoelectronic sequence, lambda being the coupling constant for the interaction between the two electrons, is summed by the ansatz of a simple analytic function of class D (Darboux). Stationarity criteria are used in constructing such a function, and the basic information needed is only a few terms of the perturbative power series. The ground-state energy is evaluated with great accuracy without using any free parameter. The Darboux method is used to give an estimate of the asymptotic coefficients of the perturbative expansion. The contrast between different empirical procedures and the self-consistency of the present one is remarkable.

The radiative decay of the atomic states with LL, LX and MX vacancies in Pb created during the electron-capture decay of ²⁰⁷Bi is studied by observing the coincidences of K Auger electrons and L X-rays, L X-rays and L X-rays, and K X-rays and M X-rays using Si(Li) X-ray detectors. The measured average L X-ray fluorescence yields of double-vacancy states are compared with those of single L-vacancy states. The angular correlation between the two cascade L X-rays emitted during the decay of double L-vacancy states does not show any significant anisotropy. The radiative branching ratios, L₃L₃-vacancy states are found.

The authors have measured the isotope shift between ⁸⁶Kr and ⁸⁴Kr for six infrared laser lines. For the line at lambda =3.066 mu m 4p⁵6p to 4p⁵6s they have measured the shifts 86-84, 84-82, 82-80 and 80-78; for this line there is evidence of a volume effect.

Using a pulsed tunable dye laser either of the 6s6p ¹P₁⁰, 5d6p ³D₁⁰ or 5d6p ³Pd₁⁰ levels in Ba I could be selectively excited from the 6s²¹S₀ ground state. A simultaneously pumped broad-band dye laser provided a back-ground continuum for photographic registration of absorption spectra. By quantum defect analysis, series members and perturbing terms of 6sns ¹S₀ were extended from n=9 to n=31, of 6snd ¹D₂, from n=41 to n=52, and of 6snd ³D₂, from n=11 to n=28. In addition, a change of previous assignments is suggested for 6p², 8s, 9s ¹S₀ and 10d, 11d ³D₂. Argon or neon was used as a buffer gas. For lines going to levels with high quantum numbers (n>or approximately=12), argon gave a pressure shift to the red of about 0.3 cm^-1 per 100 Torr and neon a blue-shift of about 0.015 cm^-1 per 100 Torr.

The cross section for excitation of metastable states of helium by electron impact has been studied as a function of incident energy up to the ionization potential. The energy scale is established by determining accurately the position on the metastable spectra of the 2³S and 2¹S levels, whose energies are precisely known from spectroscopic data. The positions of the numerous resonance structures observed in the cross section are determined and the values obtained compared with the results of previous electron transmission and metastable excitation experiments. The energy of the 2²S resonance, observed in an elastic scattering experiment performed simultaneously, is found to be 19.367+or-0.007 eV. A modified Rydberg formula is used to predict energies of the n=3 and 4 resonance states, and the correspondences between the predicted and observed energies are used to suggest classifications for the observed resonances.

A modification of the Rydberg formula for atomic states is found to give quite accurate energies of terms of the type (core)(ns²¹S) for a wide variety of atoms (ground states of negative, neutral and positively ionized atoms, negative-ion resonances, autoionizing levels). It gives, for example, the energies of the lowest negative-ion resonances of the noble-gas atoms to an accuracy of 82 MeV or better, and the electron affinities of the alkali-metal atoms to an accuracy of 100 MeV or better. It can also be applied to other terms of the type (core)(nlnl'^2S+1L). An extension of the formula gives energies of configurations of the type (core)np^N, where N=1-6.

The ejected-electron spectrum of cadmium vapour has been observed at angles up to 110 degrees with respect to an incident electron beam of kinetic energy 15 to 400 eV under high-resolution conditions. Comparisons are made with earlier ejected-electron spectra, ultraviolet absorption measurements and theoretical calculations. The spectrum is found to contain some lines which are not observed in optical studies. Angular distributions are found to exhibit pronounced maxima and minima in a number of cases.

The inhomogeneous equation method is a procedure for calculating the scattering of identical particles without using wavefunctions that display specific symmetry properties under particle interchange. Exact solutions of the equation yield separate direct and exchange matrix elements which can then be combined to form the properly symmetrized amplitude. The method has been applied to the calculation of e^-+H scattering parameters using various approximations to test its practicality. Scattering lengths have been determined using truncation procedures corresponding to 1s, 1s-2s and 1s-2s-2p basis sets, while phase shifts displaying resonance-like behaviour have been calculated in the 1s-2s-2p approximation.

Inner-shell excitation of heavy ions passing through gaseous or solid-state targets is discussed in view of the influence of collisional quenching. An apparently dominating process for collisional quenching is thought to be the capture of target electrons into projectile vacancies. This process successfully explains the oscillatory behaviour which is found for the K-shell photon yield of swift chlorine ions passing through solid foils as a function of the target atomic number.

From a knowledge of the minima r₀ of the effective potential of the two electronic states of a transition for a vibrating-rotating diatomic molecule having rotational quantum number J, together with a knowledge of the equilibrium internuclear distances, a criterion has been used to determine the influence of vibration-rotation interaction on Franck-Condon factors in the case of astrophysically important band systems.

The collision-induced translational-rotational far-infrared absorption of nitrogen has been measured for the spectral range 30 to 400 cm^-1 for pressures up to 7 kbar, or densities up to 800 amagat. These results are discussed in terms of absorption processes arising from binary, ternary and quaternary collisions and the data are used to determine an estimate for the absolute value of the quadrupole moment of a nitrogen molecule of mod Q mod =(1.21+or-0.09)*10^-26 esu.

The S-matrix of atom (electron)-diatom scattering is related to one- and two-particle field-theoretical amplitudes. Equations are obtained for generalized effective potentials describing the simultaneous excitation of both internal molecular degrees of freedom, and for targets in any initial vibro-rotational state. It is further shown that a combination of the present approach and of Rabitz' decoupling scheme (1972) can lead to a completely uncoupled description of the scattering process.

The ionization produced by Xe⁺, Kr⁺ and Ar⁺ ions during passage through thin targets of H₂, N₂, O₂ and CO has been investigated by the mass spectrometric analysis of the secondary ion products. Cross sections for the formation of particular secondary ions have been determined within the energy range 4-45 keV. The results show that, although fragmentation is always significant, non-dissociative processes generally account for over 70% of the molecular ionization. When accidental near-resonant charge-transfer processes are possible such processes are even more important. The behaviour of the non-dissociative cross sections is shown to be consistent with the simple adiabatic hypothesis.

An argon wall-stabilized arc operating at an axial temperature of 13800K and electron density of 2.1*10²³ m^-3 has been used to study the Stark-broadened wings of Lyman- alpha at wavelength separations from the line centre hitherto unexamined. Absolute calibration techniques using black-body-limited lines and hydrogen concentration measurements using HB have been applied. Comparison has been made of the experimental profiles with the theories of Kepple and Griem (1968) and Vidal et al. (1973). Satisfactory agreement is obtained with the latter theory, apart from considerable asymmetry which is observed to extend over the whole of the measured profile. Two satellite features have been observed in the red wing at 3.7 and 19 nm from the line centre and these are attributed to an argon-ion quasi-molecular perturbation.

The principal mechanism of cadmium ionization of a positive-column helium-cadmium laser discharge has been determined. Use has been made of the dip in the radial profiles of metal-ion states which results from the high metal ionization rate in such a discharge. The constancy of the dip with changing cadmium partial pressure indicates that helium ions and metastable atoms are of secondary importance in ionizing the cadmium, and that electrons are the primary source of metal ionization. A more detailed examination over widely differing discharge conditions supports this conclusion.