Table of contents

The 22nd conference of EGAS, the European Group for Atomic Spectroscopy, took place in Uppsala, Sweden, July 10–13, 1990. The conference was hosted by atomic and molecular spectroscopy groups at the Department of Physics of the University of Uppsala and was attended by 340 physicists from 26 countries.

EGAS conferences include survey lectures by invited speakers as well as contributed papers (oral and poster) on pure and applied atomic and molecular spectroscopy and related topics. The thirteen invited lectures have been prepared for publication by the authors and are presented in this issue of Physica Scripta.

The conference organizers thank all sponsors, especially the Nobel Committee for Physics, the Natural Science Research Council (NFR), the Nordic Institute for Theoretical Atomic Physics (NORDITA) and the Nordic Committee for Accelerator-based Research (NOAC), for supporting the 22nd EGAS meeting.

We review our recent work on the nonclassical radiation field of a one-atom maser. The maser cavity is cooled to 0.5 K to exclude thermal photons and has a quality factor of 3 × 10¹⁰. Velocity-selected Rydberg atoms pump the maser. The field inside the cavity is measured via the fluctuations in the number of atoms leaving the cavity in the lower maser level which are up to 40% below the Poisson level. This corresponds to photon-number fluctuations 70% below the vacuum-state limit. The one-atom maser is the only maser system which leads to nonclassical radiation even when pumping processes with Poissonian statistics are used. We analyse and propose new experiments based on the one-atom maser leading to new studies of the quantum measurement process.

The use of atomic data in contemporary stellar spectroscopy is illustrated by a number of examples of recent applications. The needs for extended and improved data are stressed.

Optical molasses is a three-dimensional (3-D) configuration of laser beams used to laser-cool and to viscously confine neutral atoms. Atoms laser cooled in optical molasses reach temperatures much lower than the limit given by the original theories of laser cooling based on the Doppler effect. This cooling below the Doppler-cooling limit is now seen as being due to new laser cooling mechanisms not considered in the original theories. The dependence of the atomic temperature on parameters such as laser intensity and detuning shows good agreement between calculations performed in 1-D and experiments performed in 3-D. For cooling of Na and Cs atoms, the lowest observed temperatures correspond to rms velocities between three and four times the single photon recoil velocity. For Cs the temperature is 2.5 ± 0.6 μK and is the lowest temperature ever measured for 3-D cooling.

High-resolution spectroscopy of negative ions can yield information about their structural and dynamic properties. Recent progress in the study of structural properties of negative ions is reviewed with emphasis on selected atomic (H^-, O^-, F^-, Cl^-, Be^-, Mg^-, Ca^-) and molecular (FHF^-, OH^-, C₂^-, NH^-) systems. The dynamic aspects are treated with emphasis on vibrational (NH^-, PtN^-) and rotational (CH₂CN^-) autodetachment processes.

Different computational schemes for relativistic many-body calculations are reviewed and analysed from the view of quantum-electrodynamics, in particular the commonly used "no-virtual-pair approximation" (NVPA). The apparent gauge dependence of the electron-electron interaction, obtained from the exchange of a single virtual photon, is discussed in the light of two-photon exchange. Numerical results obtained in the NVPA scheme are discussed and some possibilities of going beyond that level are indicated.

No abstract supplied.

In the presence of a strong state magnetic field, the classical dynamics of a Rydberg atomic state turns chaotic. This has important consequences on the energy levels and eigenstates of the quantum system. These are analysed in connection with the recent experimental results.

We discuss new aspects of generating and observing electronic wave packets in Rydberg systems. A new scheme of observing wave packets in a pump and probe configuration with time-delayed correlation broad-bandwidth laser pulses is proposed and wave packet generation in near threshold multiphoton ionization is discussed.

Antiprotons stopping in H₂ form antiprotonic hydrogen, atoms of protons and antiprotons bound by their electromagnetic interaction. Antiprotonic hydrogen atoms are formed in high Rydberg states from which they deexcite by external Auger processes and by radiative transitions to the low-lying energy levels. The levels are shifted and broadened due to strong interactions between the two particles. The strong interaction shift and width of the 1S ground state and the width of the 2P state have been determined in recent experiments at the Low-Antiproton-Ring (LEAR) at CERN. The strong interaction effects can be understood quantitatively by including a meson exchange potential (known from nuclear forces) in the Hamiltonian. This meson exchange potential is known to require the existence of deuteron-like bound states of protons and antiprotons, often called baryonium. Baryonium resonances had beed searched for in numerous experiments but without any conclusive evidence for their existence. It is shown how a detailed understanding of the atomic cascade before annihilation has helped to find a new resonance which is likely such a baryonium resonance.

A short description of the ESRF, a dedicated 6 GeV high-brilliance synchrotron radiation source, which is under construction in Grenoble, is presented. The new features of this source, namely the low emittance of the storage ring and the large number of insertion devices, are emphasized. The present status of the project, and in particular the scientific plans for the use of the source, which will be operational in 1993-94, are discussed.

Exteme-ultraviolet (X-UV) absorption spectroscopy has gained impetus in recent years, spurred on by a growing interest in the physics of core excited atomic, molecular and solid species. Progress in this field has been helped in no small measure by developments in X-UV light sources. One such source is the laser-produced plasma which, by suitable choice of target material, can be used to produce a clean, line free continuum virtually throughout the X-UV and V-UV spectral regions from 40-2000 Å. We briefly address here the issues surrounding the origin and characteristics of laser-plasma continuum light sources. In addition we review progress to date on the application of these sources to the study of the X-UV photoabsorption spectra of atoms, ions and molecules.

Recent progress in inner shell vacuum ultraviolet spectroscopy of free atoms will be exemplified by the discussion of (i) the autoionization of the Ar, K and Ca 2p⁵ 4s, 3d resonances, (ii) electron-electron coincidence studies of the decay of rare gas core resonances, (iii) Li 1s conjugate shake-up processes and (iv) angle resolved electron spectroscopy of aligned Li atoms.

A brief account is given of some recent developments in the use of ultra-soft x-ray emission spectroscopy for studies of electronic structure and excitation dynamics. In particular the novel technique of using monochromatized synchrotron radiation for the excitation of the emission is discussed and some key work presented. Also, photon emission studies in the ultra-soft x-ray range of charge transfer in slow collisions between highly charged ions and atoms are presented.

No abstract supplied.