Table of contents

A recent calculation by Tsonchev and Goodfriend (1992) of the binding energy of a hydrogenic impurity in a quantum well wire employs a novel method of imposing the boundary condition at only a finite number of lines on the surface of the wire. The author points out that, in several cases, the boundary condition in reality is imposed everywhere on the surface of the wire. In these cases, the approximation aspect of the method proves to be illusory in the sense that the imposition of the boundary condition is exact.

A zero-order approximation is made to energy levels of the hydrogen atom in magnetic fields including Landau levels and Bohr levels by using gauge transformation and gains perturbation matrix element expressions.

Total cross sections for single and double ionization of helium by alpha particles of incident energy 50 to 1280 keV u^-1 are presented. The continuum distorted-wave eikonal initial state (CDWEIS) approximation is used throughout. Corrected double ionization total cross sections are also presented. The semiclassical independent-even (IEV) model is adopted and an open-shell radially correlated two electron wavefunction is used for the initial bound state. The single ionization results fall below the experimental values; this is attributed to the neglect of ionization-excitation in the authors' theoretical calculations. The effect of electron capture to the continuum of the projectile (ECC) on double ionization cross sections for slower projectiles is briefly examined.

A double peak structure is predicted in the spectrum of electrons which are emitted from the projectile in the backward direction in collision with heavy target atoms. The calculations have been performed within the electron impact approximation and the strong potential second Born theory for hydrogen-like light projectiles colliding with Ar and Xe. The structure in the electron loss peak is only present in a certain range of intermediate collision velocities. It is sensitive to the electronic density distribution in the target and may therefore serve as a tool for investigating atomic fields in gaseous and solid targets.

Several errors in the theory of the angular correlations dealing with the electron-impact excitation of hydrogen atoms to n=3 levels and with the detection of the cascade Lyman- alpha photon in coincidence with the scattered electron are noted and corrected. In one case, a state multipole, derived from measurements of the circular polarization of the photon, has to be substantially readjusted.

The authors demonstrate three new X-ray lasers in neon-like zirconium, niobium and bromine which lase on 3p to 3s transitions. By observing the wavelengths and relative intensity of the lasing lines they hope to shred some light on the anomalous lasing in neon-like yttrium, where one laser line dominates the spectrum. In this work they report the wavelengths of five new lasing lines in bromine and six lasing lines each in zirconium and niobium.

The gf values for transitions between the ²P⁰ and ²S, ²D states of some low-lying configurations have been investigated for the aluminium isoelectronic sequence up to Ca VIII. Both intra- and inter-complex electron correlations have been included within the configuration interaction approach. Two self-consistent-field methods which differ in accounting for relativistic effects are used to generate one-electron orbitals. Comparison with other available theoretical and experimental data is presented showing fair agreement.

For pt.I see ibid., vol.26, no.8, p.1391-402 (1993). Trends in the behaviour of gf values among the gallium isoelectronic sequence up to Sr VIII have been studied for transitions between ground 4s²4p ²P⁰ and some low-lying excited ²P⁰, ²S, ²D states. The configuration interaction approach has been used to account for electron correlations. The one-electron orbitals has been generated using two self-consistent-field methods which differ in their treatment of relativistic effects. Fair agreement was found with available experimental and theoretical data.

For atoms with a central field in the Dirac-Foldy-Wouthuysen-Tani formalism, the authors find that an El matter-field coupling of the form qs.A*p/2m²c² appears with qA.r in the length gauge. In principle, this gives an alternative source of spin-assisted contributions to lanthanide transition intensities. Time reversal and parity selection rules are used to categorize such contributions as well as those from the standard terms in the Judd-Ofelt theory of lanthanide transition intensities.

The theoretical investigation of the inner 3s photoionization of the Mn atom with dependence on both the spin of the residual ion and multielectron correlation influence is performed for the first time. A set of characteristic features in this dependence is discovered. The features are considered to be common features for various atoms having multielectron semifilled shell(s) like the 3d⁵ shell of the Mn atom.

Ejected electron of atomic Cs have been measured at the 4d excitation resonances and above the ionization threshold using monochromatized synchrotron radiation. The spectra have been analyzed by comparing with the MCDF energy calculations and with previous experimental results. The resonance states were found to decay prominently via spectator Auger decay accompanied by transitions where the spectator electron shakes up during the decay. In the normal Auger electron spectra the shakeup structures mainly originate from the shakeup transitions accompanying the primary photoionization. Configuration interaction plays an important role in the spectra as well.

The time-dependent complex coordinate Floquet method was developed for the study of nonlinear phenomena observed for atoms (or small molecules) in strong laser fields. On the basis of this method and by taking use of the special definition of the inner product for nonHermitian operators a simple time-independent expression for the probability to obtain high harmonics was derived. This novel formula is used to investigate the phenomenon of harmonic generation for a model potential representing a single electron in the presence of an intense laser field. The parameters of the one-dimensional potential are chosen to fit two electronic states of the xenon atom. Numerical results indicate the existence of a correlation between harmonic generation and other nonlinear effects occurring in this system such as avoided crossings of Floquet resonance states as the field strength amplitude is varied. The harmonic generation spectra obtained by the model presented here qualitatively agree with experimental results on rare gas atoms placed in strong laser fields.

Double photoionization of a randomly oriented free atom by circularly polarized light produces photoelectron pairs with the ability to distinguish a right-handed coordinate frame from a left-handed one. This chirality, a new manifestation of electronic correlation, causes a circular dichroism in multiply differential cross sections. Necessary kinematical conditions for the observability of a finite chirality of a photoelectron pair are worked out and discussed. Results of numerical calculations for He and H^- show the amount of circular dichroism to depend strongly: (i) on the choice of wavefunctions used, especially on the description of correlation, (ii) on the energy distribution of the photoelectrons, and (iii) on the light frequency. In particular, the authors have found a critical frequency where the dichroism changes sign. The threshold behaviour has been analysed within the frame of the Wannier-Peterkop-Rau theory.

The L₂₃-VV Auger spectra for phosphorous atoms in the PH₃, PF₃ and PCl₃ molecules have been recorded following 2p core-hole ionization induced by photons with energy in the range 150-170 eV. The chlorine L₂₃-VV spectrum for the PCl₃ molecule has also been recorded. The spectra have been interpreted with the aid of molecular Auger calculations. Differences due to chemical effects are identified and a valuable insight is gained into the major pathways available for Auger decay resulting in complex spectral profiles. Predictions are made for the phosphorous 2p inherent photoelectron linewidth in these molecules.

The authors consider the charge cloud distribution of heavy atoms after impact excitation by polarized electrons. A general formula in terms of state multipoles is derived and interpreted with regard to ratios of principal axes and three independent angles of rotation. Finally, the theory is illustrated by numerical results for excitation of mercury and thallium.

Numerical calculations are presented of harmonic generation and phase matching in a rare-gas-like plasma. A simple model for the atomic dynamics is used, in which tunnelling ionization is assumed to be the dominant process. The nonlinear tunnelling current generates a series of odd harmonics of the fundamental radiation, which then propagate through the ionizing plasma. The use of a simple model for the atom makes it possible to solve the full time-dependent wave equation, and this allows direct investigation of phase matching effects due to free electrons. Such a treatment is necessary in the high-intensity, short-pulse limit, where conventional slowly-varying-envelope calculations are not valid. The authors investigate the pressure dependence of the generation efficiencies, and also observe blueshifting of the higher-order harmonics.