Table of contents

By applying bipolar electric-field pulses of about 10 V cm^-1, dE/dt approximately=10⁹ V cm^-1 s^-1, the authors have demonstrated the conversion of laser-excited Na(nd) Rydberg states (n=30-38) to high-n₁ Stark states that lie at the top of the n manifold. These states correspond in zero field to orbits of the highest allowed angular momentum l. This transition phenomenon is believed to play an important role in the microwave electric-field ionisation of non-hydrogenic atoms.

The X state in Ca is identified as 4s5g ¹G₄ at 44874.5+or-0.2 cm^-1, and the upper states in the observed transitions are reassigned to the 4snh ¹H₅ series. The simple polarisation theory gives surprisingly good agreement with experiment for all the observed transitions. The extracted polarisability of 75.3+or-0.4 a₀³ is in excellent agreement with values calculated from oscillator strengths.

Strong variation of excited levels ionisation cross sections with photon energy is demonstrated for nd ²D levels of Rb and Cs. The results of calculations proved to be sensitive to the choice of used approximation.

The angular distribution of Balmer- alpha emission excited by electron impact on H₂ has been measured and compared with the results of polarisation measurements. A new factor, r, instead of a polarisation degree, has been presented to describe the anisotropy of emission of atomic radiation following dissociative excitation of molecules.

It is pointed out that heavy atoms (i.e. those which have spectroscopically resolvable fine structure) are not required for optical measurements of electron polarisation. A polarimeter which uses helium gas instead of heavy-metal vapour is proposed, and several experimental details are discussed.

The invariance properties of the Demkov-Ostrovsky (DO) equation are analysed. This equation models the n+l filling rule of the atomic Aufbau principle. Contrary to a claim by Ostrovsky and contrary to generally known quantum problems, the degeneracy structure of the quantum number n+l in this model is not associated with the representation of a finite-dimensional Lie algebra. It is found, however, that the degeneracy algebra does not close under the usual commutation relations, but under a generalised set of commutation rules. The properties of the new algebra are closely examined. It is shown that the characteristic 'period doubling' in the DO model follows from the structure of this algebra. It is also shown that the two-dimensional analogue of the DO equation admits an SO(3,2) dynamical group which, however, allows more states than the physically required ones. Nevertheless, by a redefinition of the quantum labellings, one obtains a mapping to the appropriate state diagram corresponding to the Aufbau chart.

A non-local model potential nu _M, which approximates the interaction of the 1s and nl electrons in 1snl ³L levels of Be III to high accuracy, is used to construct an effective two-electron Schrodinger equation for 1s2snl ⁴L and 1s2pnl ⁴L core-excited levels of Be II. Wavefunctions for quartet levels of Be II are found by a configuration-interaction expansion in terms of anti-symmetrised products of eigenfunctions of nu _M and wavelengths, transition probabilities and radiative lifetimes are calculated. Some outstanding lines in the beam-foil spectrum of beryllium are discussed.

Calculations are described of the interaction between the nsnp⁶²S term and the ns²np⁴md/ epsilon d²S series in atoms isoelectronic with the halogens, particularly the rare gases. For the halogens, it has been found earlier that the interaction with the continuum d series is crucial for a correct description of the term structure. A similar, although weaker, effect of the continuum is established for the rare gases. Detailed results for the admixture of nsnp⁶²S in bound and continuum d states are reported for Cl I, Ar II, K III and Kr II. Only in K III is the effect of the continuum found to be negligible. The present results are important for the interpretation of satellite structures connected with the ejection of an ns electron from the rare gases. It is shown that there is good agreement between the present calculations and the satellite intensities in photoelectron experiments. The experimental uncertainties in photoelectron experiments are at present the limiting factors in the comparison and the need for better experimental values in order to test the calculations is stressed. Disagreements are found between the calculations and the results of (e, 2e) experiments. These disagreements are attributed to difficulties in the interpretation of the (e, 2e) experiments.

It is shown that the Compton profile functions which describe Compton scattering from polarised atomic electrons are independent of the scattering angle when the direction of polarisation is perpendicular to the incident photon direction. Explicit calculations of these functions for hydrogen-like atoms are given as well as the angular integrals for J(P_iz', theta ) (through j=⁵/₂) when the radial wavefunctions are not known. Since for other directions of electron polarisations the profile functions are dependent on the scattering angle, the importance of the profile functions being independent of the scattering angle is discussed.

The 1750 Å mercury absorption band is analysed. The temperature dependence of the profile is studied and interpreted in the framework of the quasi-static theory. The energy curve of the ground state of Hg₂ being available, the upper-state potential curve as well as the oscillator strength of the transition are derived between about 3.2 and 3.6 Å. Additional information about the upper-state energy curve is drawn from the analysis of the vibrational structure of the band. In view of the results obtained it seems reasonable to attribute this 1750 Å absorption band to transitions ending at the ³ Sigma _u⁺ Rydberg state arising from Hg(7³S₁)+Hg(6¹S₀).

The problem of calculating the bound-state energies of a molecular dimer, consisting of any two diatomics, treated as rigid rotors, is formulated. Full use is made of relevant symmetry properties. The R-matrix propagator and de Vogelaere methods are used to integrate the resulting coupled equations, and their convergence properties are compared. Results obtained for the Ar-HCl dimer are found to be in excellent agreement with previous calculations.

The authors report calculations of the energy level structure of the H₂-H₂ dimer in which the coupled equations have been numerically integrated. The R-matrix propagator and de Vogelaere algorithms have been used, and their respective convergence properties are briefly discussed. The convergence of the eigenvalues with respect to the size of the rotational basis set is also illustrated. Satisfactory numerical agreement is found with calculations based upon the secular equation method. Three independent ab initio potentials are studied. The recent CI potential of Meyer and Schaefer (1983) and Schaefer and Liu (1983) is found to give the best agreement with spectroscopic measurements, although a small shift of the position of the isotropic potential minimum is indicated.

The electronic excitation in collisions of potassium with rare gases (Ne, Kr and Xe) has been studied by measuring the dispersed fluorescence between 1300 and 9000 AA and the energy dependence of the fluorescence for some of the excited states. From these measurements for several collision energies the calibrated spectra, and the absolute emission cross sections for the K(4p) excitation and the Xe(6s) excitation have been deduced. A new theoretical model based on the interaction of the valence electron with the rare-gas atom is described. The properties of this interaction are found to be responsible for the qualitative features and with reasonable accuracy for the quantitative behaviour of the cross sections measured in collisional excitation experiments.

Cross sections for the elastic scattering of electrons by hydrogen atoms in a laser field have been calculated. Both direct and exchange amplitudes have been computed in the Born and Glauber approximations. The Franco-Halpern modification of the Ochkur approximation has been used to evaluate the exchange amplitudes. Differential cross sections are presented and discussed for electron energies of 100 eV and 54.4 eV, and for laser field orientations parallel and perpendicular to the direction of incidence of the electrons.

For pt.III see J.Phys. Soc. Japan, vol.52, no.1, p.84 (1983). The relative differential cross sections of electrons scattered by gaseous As₄ at 300 degrees C were measured by a cross-beam method at incident energies of 100 and 500 eV and at scattering angles between 2 and 135 degrees . Calculations based on the independent-atom model including intramolecular double scattering and polarisation accounted for the measured cross sections; they were used to normalise the measured relative cross sections.

The R-matrix method is used to calculate the collision strengths for the electron excitation of the ground state of O VII to the 2³S and 2³P⁰ states. Results are presented for calculations in which the five lowest states (all n=1 and n=2 states) were included as target states and also for calculations in which the eleven lowest states (all n=1, n=2 and n=3 states) were included. The five-state calculations for the 1¹S-2³S transition give many series of large resonances of the form 1s2lnl' converging to the other n=2 thresholds. For the eleven-state calculations but for the eleven-state calculations there are also significant resonances of the form 1s3lnl' converging to the n=3 thresholds. Resonance effects are quite small for the 1¹S-2³P⁰ transition.