Table of contents

Preliminary measurements in the 10-1000 AA spectral region establish the electron-beam-sliding-spark device as an intense line and continuum emitter of soft X-rays.

A controlled raising of discrete levels into the far continuum is achieved within the configuration average Hartree-Fock scheme by acting on the valence electron of Cs I. The LS-dependent scheme is also considered, in which 4d⁹4f ¹P-based levels do not rise above the associated 4d thresholds. It is inferred that controlled transfer of oscillator strength to a 'shape resonance' in the 4d⁹ epsilon f ¹P continuum will occur.

The authors present satellite photoelectron spectra from the outer shell of argon whose binding energies range from 32 to 43 eV, using synchrotron radiation in the 40-80 eV photon energy region. It has been possible to obtain satellite spectra much better resolved than those previously obtained by Spears et al. (1974) as well as to observe new satellite lines appearing only at low photon energy. An assignment is proposed for all the satellites observed by the authors. These experimental results show that the 3s3p⁶²S to 3s²3p⁴ns, nd ²S transfer has been fairly well accounted for by the theoreticians, but they also show clearly that the satellite spectra following photoionisation in the outer shell of argon arise from both the 3s and 3p subshells and that the final-ionic-state configuration-interaction mechanism describes only part of the spectrum.

The alignment of the 2p_3/2 vacancy in Mg resulting from ionisation by a proton and He⁺ is calculated. The calculations are made in the Born approximation using the hydrogen-like and Hermann-Skillman models. The theoretical prediction is compared with experimental data.

The Ne K and Kr L X-ray production cross sections were measured for projectile energies of 100 to 1100 keV. The vacancy-production ratios P between Ne 1s and Kr 2p are orders of magnitude higher than calculated vacancy-sharing ratios using the Demkov-Meyerhof estimates. A calculation of P using the Nikitin formalism gives excellent agreement with the data.

Transition probabilities are evaluated for the 2s2p ³P₁ to 2s²¹S₀ transition in beryllium-like ions for Z=4-10 and Z=14, using configuration-interaction wavefunctions. The convergence of the results with respect to the basic set of orbitals is considered. The question of at what stage the Breit interaction should be included in the Hamiltonian is discussed.

The emission spectrum of indium has been photographed over the spectral range from 340 to 6500 AA using a disruptive electrodeless discharge and a spark in helium as sources. The analysis of In III has been revised and extended and now includes 4d¹⁰ns (n=5 to 12), 4d¹⁰np (n=5 to 9), 4d¹⁰nd (n=5 to 9) and 4d¹⁰nf (n=4 to 7). Polarisation theory has been applied to the 4d¹⁰ng (n=5 to 9) and 4d¹⁰nh (n=6 to 9) series and the ionisation potential deduced to be 226191 cm^-1. The dipole polarisability of the 4d¹⁰ core is estimated to be 3.45 a₀³. Most of the expected terms of 4d⁹5s5p are established for the first time.

The hyperfine-structure constants of the excited atomic levels 3d⁵4p z⁷P_4,3,2 and 3d⁴4s4p y⁷P_3,2 of ⁵³Cr have been measured by the level-crossing technique. The signs of the A factors result from the interpretation of the experimental data by means of a least-squares fit of the appropriate HFS parameters with regard to core polarisation, spin-orbit interaction and configuration mixing of the excited levels of ⁵³Cr. This interpretation yields a value of -51 MHz for the contribution of the core polarisation to the hyperfine-structure splitting of the investigated levels equivalent to -543000 G for the respective magnetic field at the nucleus.

Perturbation theory based on the frozen-core Hartree-Fock approximation in zero order is used to calculate the oscillator strength for the 1s²¹S to 1s epsilon p¹P photoionisation of helium. The method gives agreement between the dipole-length and dipole-velocity calculations to one part in one thousand. The dipole-acceleration calculations deviate from these by only 1%.

The shapes of three low-energy resonance features in the photoionisation of neutral neon are calculated along with the total cross section in the low-energy region. The lowest singly excited resonance is in particularly good agreement with experiment. The complex amplitudes in the vicinity of the lines are plotted and discussed as an aid to understanding aspects of these resonance features. The experimental absence of the 1s²2s²2p⁴3s4p line, in particular, seems to be the result of the two open-channel amplitudes' fluctuating out of phase so that the sum of the resulting partial cross sections is not measurably disturbed.

Many-body perturbation theory is applied to calculate the 4d¹⁰-subshell photoionisation cross section for neutral Cd. First-order electron-electron correlations are found to produce excellent agreement between the dipole-length and dipole-velocity formalisms, and results are in generally good agreement with recent experimental data. Relaxation effects and contributions from second-order RPAE diagrams are also calculated. A non-relativistic calculation for the asymmetry parameter beta of the photoelectron angular distribution is included.

Mercury atoms are stepwise excited to the 6s6d levels by means of a mercury lamp (6¹S₀ to 6¹P₁) and a CW tunable dye laser (6¹P₁ to 6¹D₂ or 6³D₂). The transfer of coherence (orientation and alignment) between these levels induced in collisions with noble-gas (helium and xenon) atoms is studied in a weak magnetic field by means of the Hanle effect. Values of the cross sections for coherence transfer are determined from the experimental data.

The cross sections for transfer of population from the Hg 6³D₁ level to the other levels of the 6s6d configuration, induced by collisions against N₂ molecules, are measured using, for the selective excitation of metastable 6³P₀ Hg atoms, a tunable dye laser with frequency doubling producing pulses of 2967 AA light. The following results are obtained: sigma (³D₁ to ¹D₂)=100+or-20 AA², sigma (³D₁ to ³D₂)=30+or-7 AA², sigma (³D₁ to ³D₃)=33+or-10 AA², sigma (¹D₂ to q)=150+or-50 AA², sigma (¹D₂ to q), being the cross section for population transfers from the 6¹D₂ level to all Hg levels besides the 6³D₁ level.

Line-broadening parameters corresponding to the collisional relaxation times T₁ and T₂ have been measured for the rotational transition 3₁₂ from 3₁₃ (28.975 GHz) of the astrophysical molecule CH₂O when mixed to make dilute gas solutions with H₂ and He. The method employed static absorption linewidth measurements with a high-resolution Stark spectrometer. Corrections necessary to account for instrumental and other lineshape distortion effects which arise with this technique are described. Results which disagree with those of some previous workers are presented.

The authors formulate the T matrix of the K-shell ionisation process induced by a heavy charged particle in the framework of the semiclassical approximation using correct hyperbolic trajectories. The ejected K electron is described by relativistic (Dirac) wavefunctions. Explicit expressions for the form factor are given. Several model calculations for differential cross sections are presented. Comparisons with actual experiments are also given.

In the collision system Xe-Ag, the thresholds for excitation of quasimolecular L radiation and characteristic Ag L radiation have been found to lie at about 5 MeV and 1 MeV, respectively. These results are discussed on the basis of ab initio calculations of the screened interaction potential and the electron-correlation diagram.

The analytic properties of the forward elastic exchange amplitude g(E) are studied as a function of the incident electron energy E for electron scattering by atomic hydrogen. The authors first prove that the bound-state of g_B2(E), the second Born contribution to g(E), has an infinite number of singularities due to the analytic structure of the off-shell first-order exchange matrix element. These singularities are (i) poles of order (n-1) at E=-1/2n² (n>or=2) associated with excited intermediate states of the target and (ii) cuts at E=-1/2n² (n>or=1) coming from all intermediate states. In addition, the bound-state part of g_B2(E) also exhibits poles and cuts at E=-2(1+1/2n)², n>or=1, arising from the integration over the intermediate momentum of the projectile. They then show that the continuum contributions to g_B2(E) lead to singularities having the same location as those coming from the bound states, so that the interplay between bound and continuum singularities is very important.

The Born approximation is used to calculate total and differential cross sections for one-electron ionisation of H^- by electron impact. Polarised-orbital wavefunctions are employed for the H^- continuum state, whilst the sensitivity of the cross sections to the H^- bound state is investigated by using 20- and 33-parameter correlated wavefunctions. For the total cross section, agreement between theory and experiment is satisfactory for impact energies greater than about 100 eV. The differential cross sections are shown to be highly sensitive to the bound-state function and in particular to the asymptotic behaviour of the functions.

The author has carried out a detailed study of positron annihilation in helium, argon and helium+argon systems and investigated systematically the influence of temperature, electric and magnetic fields. It is found that increasing the temperature or electric field decreases the annihilation decay constant while the magnetic field increases this constant. A model is suggested to estimate the decay constant of mixtures. Comparison with experimental observations is made wherever possible.

Some general features of the quasi-energy dependence on the periodic field frequency and amplitude are examined assuming the discrete character of the quasi-energy spectrum. Jump discontinuities are found in the frequency dependence of the quasi-energy and connected with them band structure of the quasi-energies. A notion of mean energy of a system in a periodic field is introduced and relations between the mean energy and the quasi-energy are investigated. As examples the quasi-energy zones for a two-level system and a rigid rotator are calculated.

For the model of a plane rotator in an intense circularly polarised wave the response of the quantum system to the intense field and a weak monochromatic perturbation is obtained. The authors calculate the cross sections for coherent and Raman scattering of the strong field and cross sections for elastic and inelastic scattering and absorption and emission of the weak field.