P G Burke

Atomic data for opacity calculations. II. Computational methods

For pt.I see ibid., vol.20, p.6363-78 (1987). A general description of the data requirements for opacity calculations has been given in paper I. The present paper gives a detailed description of the methods being used in a collaborative effort which is referred to as the Opacity Project. The close-coupling approximation of electron-atom collision theory is used to calculate energies and wavefunctions for bound states, oscillator strengths, photoionisation cross sections and parameters for line broadening by electron impact. The computations are made using the R-matrix method together with new codes for calculating outer-region solutions and dipole integrals. Use of these techniques provides an efficient means of calculating large amounts of accurate atomic data.

Electron-molecule interactions. IV. Scattering by polyatomic molecules

For pt III see abstr. A70819 of 1972. The theory of scattering of low energy electrons by closed shell polyatomic molecules is developed. Coupled inhomogeneous differential equations are obtained describing the motion of the scattered electron in the fixed nuclei approximation. The symmetry group of the molecule is used to reduce these equations to their simplest form and expressions for the total, differential and momentum transfer cross sections are obtained. A transformation to the laboratory frame is then derived and this is used to obtain expressions for the rotational excitation cross sections in terms of the S matrix calculated in the fixed molecular frame. Special emphasis is given in this paper to the C2v and Oh symmetry groups and the equations describing electron scattering by water molecules are discussed in some detail.

Electron scattering by atoms and ions using the Breit-Pauli Hamiltonian: An R-matrix approach

The R-matrix method describing the scattering of low-energy electrons by complex atoms and ions is extended to include terms of the Breit-Pauli Hamiltonian. An application is made to the astrophysically important 1s22s2 1S0e-1s22s2p 3P1o transition in Fe XXIII, where in the most accurate calculations carried out all terms of the 1s22s2, 1s22s2p and 1s22p2 configurations are included in the expansion describing the collision. This gives up to 28 coupled channels for each total angular momentum and parity which are solved on a CRAY-1. The collision strengths are increased by more than a factor of two from their non-relativistic values at all energies considered.

Photon and electron collisions with atoms and molecules

Excitation of Atoms by Electron Impact: Current Status and Future Prospects K. Bartschat. Electron-Helium Correlation Studies A. Crowe. Ionization of Atoms and Ions by Electron Impact R.H.G. Reid. R-Matrix Theory of Electron-Molecule Collisions L.A. Morgan. Electron Collisions with Molecules on Metal Surfaces J.P. Gauyacq, et al. Recent Measurements of Differential Cross Sections for Electron-Molecule Collisions at Low Energies M. Allan. Dissociative Recombination: New Developments Stimulated by Ion Storage Ring Experiments A. Suzor-Weiner, et al. One and Two-Electron Resonances in Molecular Photoionization R.W. Zurales. Double Photoionization of Helium M. Pont, R. Shakeshaft. Multicolor Photoionization of Atoms with an IR Laser and Its Higher UV Harmonics V. Veniard, et al. Stabilization of Atoms in Ultra-Strong Laser Fields M. Gavrila. Laser Assisted and Laser Produced Scattering J.H. Sanderson, W.R. Newell. R-Matrix-Floquet Theory of Multiphoton Processes M. Dorr. Resonance Effects in Multiphoton Ionization N.J. Kylstra. Multiphoton Processes in a Two-Electron Atom Using a Cray T3D K.T. Taylor, et al. Application of Parallel Computers to Electron Molecule Scattering Calculations N. Sanna, F.A. Gianturco. 7 Additional Articles. Index.

Electron-impact-excitation collision strengths for Be-like ions: II. Intermediate-energy region and collision rates

Abstract Intermediate-energy collision strengths calculated using the R-matrix method are presented for four Be-sequence ions, C III (2.6–8.0 Ry), O V (4.4–12.0 Ry), Ne VII (8.4–20.0 Ry), and Si XI (11.0–34.0 Ry). The six ionic states (2s2) 1S, (2s2p)3P0, 1P0 and (2p2)3Pe, 1De, 1Se, corresponding to ten fine-structure levels, are included, leading to 29 independent transitions per ion. High-energy analytical expressions have also been calculated for the collision strengths. These results have been combined with previously published low-energy collision strengths to deduce effective collision strengths (that is, collision rates) for ranges of electron temperature appropriate to the four ions.

Electron-molecule interactions. III. A pseudo-potential method for e--N2 scattering

For Pt. II see Abstr. A43069 of 1970. The low energy scattering of electrons by molecular nitrogen is calculated using a pseudo-potential method. Expressions for the cross sections in terms of the calculated S matrix elements are developed and momentum transfer cross sections are obtained which are in good agreement with experiment. The theory is then extended to predict rotational excitation cross sections and differential cross sections. It is suggested that this approach may enable electron molecule collision cross sections involving complex molecules to be calculated.

Electron - atom scattering at low and intermediate energies using a pseudo-state/ R-matrix basis

The use of a pseudo-state expansion within the standard low-energy R-matrix framework to facilitate the study of electron scattering by complex atoms and ions at both low and intermediate energies is discussed. Electron scattering from atomic hydrogen is considered as an example, and results for elastic scattering phase shifts and excitation cross sections are found to be in excellent agreement with recent IERM results in these energy regions. The advantage of this procedure is that existing computer codes, which have been developed over many years, can be directly extended to study electron scattering from a general N-electron target atom or ion.

Electron-molecule interactions. II. Scattering by closed-shell diatomic molecules

For pt. I see ibid. vol. 3, no. 5, 636 (1970). The theory of electron scattering by closed-shell diatomic molecules, assuming that the molecule is constrained to be in its ground electronic state, is developed. To simplify the analysis it is assumed that the molecule does not vibrate or rotate during the collision and it is then shown how rotational excitation cross sections may be obtained from the asymptotic form of the scattered electron wave function. A general computer code based on this formalism and using single-centre wave functions has been written and it used to study e--N2 collisions at low energies. A low energy 2 Pi g resonance is found in agreement with recent experiments.

Correlation in the elastic and inelastic S-wave scattering of electrons by H and He+

Equations are derived describing the scattering of electrons by hydrogen-like ions when electron-electron correlation terms are added to the close-coupling expansion of the total wave function. The 1s, 2s and 2p terms are retained in the latter expansion, while up to sixteen correlation terms are retained in the former expansion. Provided the incident electron energy is insufficient to excite the third quantum level of the target the resultant solution satisfies a minimum principle. The numerical solution of the equations is discussed and results are presented for elastic and inelastic S-wave transitions in e--H and e--He+. Above the energy where the minimum principle applies it is possible to obtain physically significant results by varying a non-linear parameter in the wave function in order to avoid singularities in the solution.

The scattering of electrons by atomic nitrogen

Cross sections for elastic and inelastic scattering of electrons by atomic nitrogen are calculated over an incident electron energy range from threshold to 35 eV using the R-matrix method. In most of the calculations the eight target states 1s22s2p3 4S0 2D0 and 2P0, 1s22s2p4 4Pe 2Pe 2De and 2Se and 1s22p5 2P0 of nitrogen are retained in the expansion of the total wavefunction. However in some of the calculations fewer target states are retained in order to compare with the results of earlier work. Apart from energies close to the 1s22s22p4 3Pe resonance state of N- the cross sections appear to have converged well.