M Le Dourneuf

Resonant vibrational excitation of N/sub 2/ by low-energy electrons: An ab initio R-matrix calculation

The resonant vibrational excitation of

Atomic data for opacity calculations. XXIII. The aluminium isoelectronic sequence

{mathrm{N}}_{2}

Hyperspherical description of collinear reactive scattering

by low-energy electrons is used to illustrate the newly developed

Cross sections calculations for electron oxygen scattering using the polarized orbital close coupling theory

R

Dissociative recombination of CH

-matrix theory of vibrational excitation and dissociative attachment of Schneider, Le Dourneuf, and Burke. The ab initio calculations are performed which clearly illustrate the role of the internal states in describing these excitation processes and support the authors contention that the essential physics is completely contained within a Born-Oppenheimer treatment of the total molecular Hamiltonian.

Hydrogen atom in crossed electric and magnetic fields: transition from weak to strong electron-proton decentring

As a contribution to the international Opacity Project, large numbers of term energies, oscillator strengths and photoionization cross sections have been computed for Al-like ions of astrophysical interest (Al I, Si II, S IV, Ar VI, Ca VIII and Fe XIV), using an ab initio close-coupling approach in LS-coupling. Careful comparisons with previous theoretical and experimental work show that our collisional approach allows a systematic and accurate description of plunging configurations, series perturbations and cancellations typical of these three-valence-electron systems. Even for highly ionized systems such as Fe XIV, the neglect of relativistic effects introduces limited inaccuracies ( approximately 5%) in the average term energies, and the gross features of the distribution of oscillator strengths are accurately delineated. The main contribution of the present study lies in the volume of accurate new data made available to the public through the TOPbase atomic database: 1935 computed multiplets compared to 225 observed ones, 56242 oscillator strengths and photoionization cross sections from 1296 initial states.

Atomic polarizabilities and polarized pseudo-states in the multiconfigurational approach. II. First row atoms and ions

Hyperspherical coordinates are used to describe the asymmetrical collinear reaction F+H2 to FH+H. Compound-state resonances are characterised accurately in the adiabatic approximation.

Electron impact excitation of fine-structure levels of atomic oxygen

The formulation given by Feautrier et al. (1971) for transitions induced by electron impact among ground state terms of atoms with one configuration npq is used with a slight modification by taking into account the orthogonality of the free wavefunction to the bound npq orbitals. A system of coupled integro differential equations, obtained from a modified close coupling expansion by including long range pseudo states, is solved numerically for electron incident on oxygen in the threshold region. The present results agree very closely with experiment. Independently of the evident astrophysical interest of these results (especially the excitation cross sections of the forbidden lines), the generalizations of such calculations to other systems with the same type of configuration is straightforward with this automatic code. The multichannel photodetachment cross sections of O- by dipole length and velocity formulae are also reported and discussed.

The variable-phase method in multichannel electron-atom or electron-ion scattering

Dissociative recombination of CH+ is studied by using the multichannel quantum defect theory (MQDT). The relevant electronic states were calculated by adopting the self-consistent field (SCF) and the configuration mixing (CM) methods. Particular care was taken to represent correctly the diffuse character of the excited states, especially of the two-electron excited states. The dissociative state coupled with the initial channel was found to cross the lowest potential of CH+ near the left turning point of the first excited vibrational state. The authors took into account both the p pi and d pi partial waves of the incident electron in the MQDT treatment. For this purpose, they modified the MQDT formulation by Giusti so as to fully describe the angular parts. The rate constant obtained is 1.12*10-7 cm3 s-1 at 120 K, which is about one third of the experimental value of Mitchell et al. (1978). The contribution of the d pi wave was found to be comparable to that of the p pi wave.

Isotopic effects in the collinear active FHH system

The hydrogen atom in crossed electric and magnetic fields is studied, taking full account of centre-of-mass effects and using a variational basis which does not depend on the choice of a canonical representation, in particular of a gauge. Spectra and wavefunctions are computed for strong magnetic fields. From the analysis of results, general properties for arbitrary crossed fields are deduced. For small electric fields, the most strongly bound states remain essentially centred in the Coulomb well and show only perturbative departure from cylindrical symmetry, while highly excited states may reveal a partial decentring of the electron with respect to the proton, leading to a significant electric dipole moment. Increasing the electric field induces a transition to strong decentring with a very large dipole moment. Above a state-dependent critical electric field, only strongly decentred states remain bound.