Table of contents

The best variational energies epsilon obtained to date for the weakly-bound states of muonic molecules dd mu * (L=1) and dt mu * (L=1) are calculated. A value of epsilon (dd mu *, L=1) is obtained with an accuracy that meets the requirements of muon-catalysed fusion investigations: epsilon (dd mu *, L=1)=1.972+or-0.001 eV. The energies of the 1¹S, 2³S, P, 2¹ 2³P states of the ^infinity He atom and of the 2¹P state of ³He and ⁴He atoms are calculated by the same method.

A generalised simple Vinti wavefunction for the 1s2s¹S state of He, depending on three parameters, is chosen in such a way that it is orthogonal to the ground-state function of Morse et al. (1935). The author corrects some errors in the numerical values of Eckart (1930) and Vinti (1931). The results obtained by the author's modification of Vinti's function are better than those obtained from the function of Marriott and Seaton (1957) and from the function of Das et al. (1879).

A complex quasi-energy approach is presented for accurate treatment of photo-ionisation of the H atom in strong magnetic fields. The autoionising resonances near the first two excited Landau thresholds are determined by the complex-coordinate coupled-Landau-channel method. Detailed resonant photoionisation cross sections and asymmetric line shapes are reported for the case of B=4.7*10⁹ G.

Simple and double ionisation of a strontium atomic beam have been studied with a picosecond dye laser around 565 nm with intensities ranging from 10 to 1000 GW cm^-2. Resonances observed on the different ion signals as well as time-of-flight electron energy spectra clearly show that double ionisation is a two-step process which can involve above-threshold ionisation followed by resonant ionisation of the ion.

The authors present a model for above-threshold ionisation (ATI) phenomena that includes an infinite number of continua, in which the continuum-continuum matrix elements decrease with increasing energy. The model leads to a closed-form expression for the mth photopeak amplitude. The multiphoton index k varies with laser intensity from N+m-1 to N-1 for this peak.

The absorption cross sections of HF in the vacuum ultraviolet were measured using synchrotron radiation. The observed absorption is a continuous band corresponding to the A¹ Pi from X¹ Sigma ⁺ transition.

A variable charge potential version of the classical trajectory Monte Carlo method is used to obtain charge exchange ionisation and loss cross sections for Fe^q+ (q=12-18) ion in hydrogen at energies from 10 to 400 keV amu^-1. Scaling laws for the cross sections as a function of q are given at 100 keV amu^-1. The authors also give rough estimates of the cross section for excitation of the target and discuss the distribution of captures in n, l and m_l.

It is theoretically predicted that an isolated narrow resonance in the elastic scattering of electrons by alkali-metal atoms (M) gives rise to a single maximum in the n dependence of the total cross sections of high-Rydberg atoms A** in the highest allowed angular momentum states with M if the resonance width is roughly equal to or larger than the width of a single peak of the electron momentum distribution of the Rydberg states with highest angular momentum, i.e. l=n-1. This can be used to detect the narrow resonance theoretically predicted in e-M elastic scattering at ultra-low energies.

The anomalous magnetic moment of the electron makes an non-trivial contribution of fine-structure splittings which has, nonetheless, been ignored in many ab initio calculations. This paper aims to present a straightforward derivation of an effective Hamiltonian for relativistic calculations which includes the electron anomaly, both at the Dirac-Fock level and in the Breit-Pauli approximation. It thus provides the framework for comparative studies of predicted fine structure using these two methods which are the subject of separate publications.

The sum over l and m of mod phi _nlm(r) mod ², where phi _nlm(r) is a bound-state hydrogenic wavefunction with principal quantum number n(>>1) and angular momentum quantum numbers l and m, is evaluated approximately using the Thomas-Fermi statistical approach. This approach breaks down in the region near the nucleus and in the region near and beyond the classical edge of the nth shell at r=2n²a₀/Z, with Z the atomic number. A simple correction, proposed recently by Englert and Schwinger (1984) in the context of heavy atoms, is investigated in the region near the edge. Results are presented. The sum over n and m of mod phi _nlm(r) mod ² and the sum over l and m of mod phi _nlm(k) mod ², where phi _nlm(k) is the Fourier transform of phi _nlm(r), are also evaluated using the Thomas-Fermi method.

In a recent experiment involving multiphoton ionisation of Xe it was found that the photoelectron spectrum contained peaks which corresponded to absorption of more than the minimum number of photons required ionise. The effective orders of nonlinearity, furthermore, showed a striking uniformity. The authors investigated these effects with a model approximation consisting of a single bound state and m continua. Simple analytic expressions are obtained for the quantity measured in the experiment and the limit m to infinity is obtained. The results show good qualitative agreement with experiment.

The differential-matrix Hamiltonian operator is determined for the case when atoms move in the vicinity of the adiabatic terms' intersection point of pi = Delta = Phi type. Four-dimensional Lie algebra of the symmetry operators is obtained for the particular case of the Hamiltonian. Complete separation of variables has been carried out for the corresponding system of coupled Schrodinger equations. As a result of the use of the adiabatic electron basis, one-dimensional adiabatic terms of radial motion are determined. The authors propose the realistic sense of the quasistationary states at the upper conical term and find the positions and widths for corresponding energy levels. Some limited analogy with the two-dimensional model is stressed.

Cross sections for intramultiplet transitions among the Mg(3s3p ³P_j) states induced by collisions with He(¹S) are calculated by a close-coupling treatment based on ab initio Mg(3s3p ³P)+He(¹S) potential curves. The degeneracy averaged j to j' cross sections are compared with previous close-coupling calculations of Orlikowski and Alexander (1984) based on a model potential description of the relevant electrostatic potential curves. Differences in the two sets of calculations are seen in the relative magnitudes of the 2 to 0 and 1 to 0 cross sections at low energy and in the oscillatory structure in the energy dependence of the cross sections. The results are interpreted within a fully adiabatic description which gives insight into the mechanisms involved in fine-structure-changing transitions in collisions of ³P atoms with closed-shell atoms.

The authors treat electronic excitation processes for the example of Ne⁺+Ne collisions in the energy range of 5-500 keV by solution of an effective time-dependence Schrodinger equation in the impact parameter approximation. In particular the authors present results for the 2p-2s vacancy transition and discuss the evaluation of channel and inclusive cross sections in a many-particle situation.

Multistate quasiclassical close-coupling calculations which employ adiabatic molecular data and a common electron translation factor for the lightest alkali-alkali-cation systems show systematic differences with available experimental results for charge transfer at intermediate energies. This indicates the importance of excitational charge transfer which was ignored in most previous theoretical work. The authors discuss the translation factor approach for different sorts of interstate coupling, and comment on the accuracy of the available molecular data for these systems.

The authors use an efficient matrix propagator method to solve the coupled equations describing populations of the adiabatic states of Na₂⁺ during a collision of Na⁺ with laser-excited Na(3p). Both straight-line and curved energy-conserving classical trajectories for the nuclei are used. Electronic motion is treated explicitly with a common translation factor. The radius at which the electronic angular momentum of a partially coherent mixture of Na(3p sigma _u) and (3p pi _u) becomes locked at the molecular axis is evaluated and the dependence of differential cross sections for inelastic transitions on the initial orbital alignment and orientation is discussed. The elementary mechanisms responsible for the observed effects are analysed numerically. Results are in qualitative agreement with recent experimental findings.

Total cross sections have been remeasured for 20-100 eV electron scattering from Ar, Kr and Xe, achieving an accuracy of better than 5%. In the present measurements a short collision cell of adjustable length has been used, which permitted the application of higher target pressures than previously. Consequently, a more accurate determination of this parameter was possible, resulting in more reliable data for the total cross section. It appeared that below 70 eV the present data were substantially lower (at most 10%) than the authors' previous ones and in very good agreement with the most recent experimental data of Nickel et al. (1983). Because of the influence of effusion through the cell apertures, an experimental test had to be carried out on the effective gas density as a function of the cell length. This was also of critical importance for putting the authors differential cross section measurements on an absolute scale, as will be discussed in a subsequent article.

The population of metastable mercury (6³P_0,2) states by electron impact excitation has been studied using the method of stepwise electron and laser excitation. Relative excitation functions have been determined as well as the ratios Q(2)/Q(0), Q(1)/Q(0) and Q(2)/Q(1) of the magnetic sublevel cross sections Q(M) for the 6³P₂ state. Comparison with a recent R-matrix calculation is made.

Absolute differential cross sections for elastic scattering and vibrational excitation of CO by electron impact are presented. The electron collision energy reaches from 1.5 eV down to threshold, the covered angular range lies between 5 degrees and 110 degrees . By comparing the measured angular and energy dependences with theoretical models, contributions of different interactions to the differential cross section are evaluated. For the elastic cross section, the existing value of 0.7 a₀ for the scattering length of CO is in agreement with the authors experimental results. Finally, integrated cross sections for the vibrational excitation process are found to differ substantially from electron swarm results.

A high energy resolution electron impact spectrometer incorporating a penetrating field analyser for low-energy scattered electrons has been used to study the threshold electron spectrum of carbon monoxide. Spectra are presented for the energy region from 5.8 to 19.5 eV. The assignments of the observed features are discussed. Evidence is found for effects due to long-range electron-electron correlations.

The electron impact ionisation efficiency curves of HCl and DCl have been measured with a high signal-to-noise ratio, in the energy range immediately above the first ionisation threshold (12.75-26 eV). Many structures from HCl*, DCl*, HCl^-* and DCl^-* are seen. Vibrating Rydberg states related to the configurations (3p sigma )(3p pi )⁴4s, 3d and their corresponding negative-ion states are observed. Furthermore the pair of states related to the (3s sigma )(3p sigma )²(3p pi )⁴4s and 4p levels are reported.

The authors applied the global operator of Drachman (1981) to the case of positron scattering from helium atoms. The global operator is identical to the usual delta function operator for exact wavefunctions and is expected to yield superior results in the case of approximate wavefunctions. This expectation is borne out in the present work.

Muonic X-ray intensities for the Lyman series in oxygen and of the Lyman and Balmer series in chromium have been measured in CrO₃ and in crystalline and amorphous Cr₂O₃. By means of muon cascade calculations which reproduce the measured intensities, angular momentum distributions of the captured muons have been determined for oxygen in a mu atomic level n=14 and for chromium in n=17. The Cr/O capture ratios per atom have been found to be 3.23 in CrO₃ and 2.64 in both structures of Cr₂O₃. This difference is due to the electronic bond structures. The capture probability in chromium is larger in the higher oxidation state which is in contrast to observations in some other elements.

The possible role of the reaction H^-+H⁺ to or from H+H* in populating the n=3 level of the hydrogen atoms in the afterglow plasma of a 2 m Z-pinch in hydrogen is investigated. The method used is to observe the effect of any H^- destruction on the H_alpha emission from the plasma in the region of the discharge axis, due to irradiation of the plasma by a 50 MW Q-switched ruby laser beam passing along the axis. It is estimated that not more than 35% of the n=3 level population arises from this reaction.