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Calculations have shown that the decay of the highly excited He^- 2p³⁴S⁰ takes place via a bound-free radiative transition as a narrow band of extremely short wavelength radiation around lambda approximately=317 AA, with a lifetime of tau approximately=1*10^-10 s. Given that the final state is empty, population of He^- 2p³⁴S⁰, which remains unobserved, implies the automatic establishment of population inversion. Considering the magnitude of the relevant atomic properties, two experimentally feasible pathways for preparing He^- 2p³⁴S⁰ (and similar states) are proposed.

During tunnel ionization of heavy water molecules by mean of a powerful CO₂ laser, monomer and dimer ions were produced. This prompted the authors to ask if the dimer ions can dissociate into monomer ions. They check this by a covariance mapping calculation supplemented by a hypothesis test to take care of the noise. With this test, the authors determine there is no correlation between the monomer and the dimer ions at 9.2 mu m. This improved method can be applied to other similar problems.

The authors report results of calculations on Na excitation in Na+H collisions. The values clearly support the recent measurements of Fleck et al (1991) with respect to the previous data of Howald et al (1984).

The total attenuation cross section sigma _att and the single-electron capture cross section sigma ₂₁ in collisions of ³He²⁺ with H₂ have been measured using a tandem mass spectrometer whose collision cell consists of an octopole ion beam guide. A possible scattering loss which might contribute to sigma _att is examined, and a large part of the difference sigma _att- sigma ₂₁ is attributed to the double-electron capture process. As its magnitude is as large as 10^-15 cm² at the lowest energy studied. The importance of the process is emphasized in connection with the production of fast protons through Coulomb explosion of H²⁺₂.

Electron capture by slow multiply charged ions colliding on rare-gas targets is known to populate highly excited states of the projecile with very large cross sections. For double electron capture, (n,n') series with n approximately=n' are, in general, preferentially populated. Though these states are almost completely autoionizing, important radiative decay following double capture has been reported. Recently the fluorescence from n<<n' Rydberg states has been observed. These findings are important since they strongly modify the charge and radiation balance of the multiple charge exchange reactions. The authors propose a mechanism based on post-collisional effects which feeds Rydberg states from the quasi-symmetrical doubly excited states initially populated. A simple quantitative estimate of this effect is proposed on the basis of the well known 'Barker and Berry' formula.

A procedure is described whereby coupling to the continuum is allowed for in the description of the e^--H scattering process. The method is applied to elastic scattering and its is shown that the method converges more rapidly than when only coupling to other bound states is included. Typical results are shown as a function of the basis size.

The Stark widths of ten Si III and seven Si IV spectral lines have been measured for the electron density range of 1.4*10²³ m^-3-3.0*10²³ m^-3 and for an electron temperature range of 29000-64000 K in a pulsed linear arc plasma discharge in O₂ and SF₆. Experimental values of Stark widths for ionized silicon spectral lines follow a simple dependence on the upper level ionization potential of the transition.

Auger rates, average absorption oscillator strengths (corresponding average wavelengths) and level-to-level dielectronic recombination rate coefficients describing dielectronic recombination for F-like and Ne-like germanium ions are explicitly calculated. The calculations are based on Cowan's non-relativistic multi-configuration Hartree-Fock (HFR) code which includes relativistic mass-velocity and Darwin corrections and successive subroutines for calculating average oscillator strengths and average wavelengths and dielectronic recombination rate coefficients are developed. The dielectronic recombination rate coefficients as the function of temperature of free electrons are given in an analytical form which is very convenient in practice.

A photoelectron spectrometer composed of two analysers of different types has been used in an electron-electron coincidence mode to study photo-double ionization phenomena in neon, argon, krypton and xenon. Relative partial cross sections of the lowest three double ion states measured close to threshold would indicate that the predicted state selectivity is roughly adhered to except in the case of neon. The near-threshold angular behaviour of the ejected photoelectrons did not indicate a trend dependent on the symmetry of the state of the double ion as would be expected from theory.

Elastic, inelastic and charge exchange differential cross sections are calculated for He⁺(1s)+H(1s) collisions, in the energy range 1.5 keV<or=E<or=25 keV, using a 15-state molecular treatment, modified with an optimized translation factor. The authors compare their results with previous theoretical and experimental data. Agreement with the latter is, in general, quite good, with the important exception of elastic cross sections.

A four-body continuum distorted wave approximation (CDW-4B) is introduced to investigate the resonant (RTE) and non-resonant (NTE) transfer and excitation processes which are likely to occur when fast, not-fully-stripped ions collide with atomic targets. This new theoretical approach is a unified treatment of RTE and NTE which allows the interference between these two coherent processes to be studied.

For pt.I see ibid., vol.25, no.4, p.825-37 (1992). Resonant (RTE) and non-resonant (NTE) transfer and excitation processes which occur in collisions of fast S¹⁵⁺ (1s) with H atomic targets, are investigated through a four-body continuum distorted wave approximation (CDW-4B) derived by Gayet and Hanssen (1992). The present application is a test of this new theoretical unified approach. Results are compared with previous theoretical and experimental data obtained with molecular targets for impact energies close to resonances. A first quantitative study of the interference between the two coherent processes is made using a model in which both the projectile and the target are hydrogen-like ions. For inner-shell capture from targets whose nuclear charge is comparable with the charge of the projectile, it is shown that interference effects might be significant, even at impact energies close to resonances.

The wave formulation of the impulse approximation has been applied to the case of electron capture into the ground, 2s and 2p excited states of hydrogen in collisions between protons and alkali-metal atoms sodium, potassium, rubidium and caesium. The transition matrix elements have been numerically calculated and used to determine the differential and integral cross sections for charge transfer for incident energy varying between 50 and 500 keV. Wherever possible the results have been compared with other available results.

The authors extend their previous theory of electron-polar molecule scattering to study of the inelastic scattering, accompanied by the transfer of L photons, of fast electrons by HF molecules (in the electronic ground state) in the presence of an infrared laser beam taken in the dipole approximation. A non-perturbative Floquet method is used to describe the laser-molecule interaction while the non-perturbative Volkov solution is taken for the laser-projectile interaction. The electron-molecule interaction is treated within the first Born approximation. A detailed study is made of the vibrational excitation transitions v=0 to v=1, v=0 to v=2 and v=0 to v=3 in the HF molecule for the absorption of L photons. The collisional geometry is such that the laser polarization vector in is parallel to the momentum transfer q.