D. Fussen

Theoretical study of mutual neutralisation in H+-H- collisions at low energy (0.02-20 eV)

The theoretical total cross section for mutual neutralisation in H++H- collisions at low energy (0.02-20 eV) is calculated using a quantum close-coupling treatment. The present work extends the previous study of Sidis et al. (1981-3) towards low energies. The total cross section is found to disagree with the experimental result of Moseley et al. (1970) by a factor of about three but agrees with the recent experimental data of Szucs et al. (1984). In addition general good agreement is obtained with the Landau-Zener total cross section of Bates and Lewis in the energy range considered.

One-electron charge exchange between and positive multiply charged ions. 1. Collisions

The cross section for one-electron transfer is calculated in this paper. The collisional system is treated as a three-electron one and matrix elements for the formation of excited helium in both singlet and triplet states (1S, , P and , P, D) are obtained. Close-coupling calculations were done for the 27 (1S, , P and , P, D) final states covering the range 1 - of the relative collision velocity. An approximation is used for the effective potential of and Coulomb Greens functions are used to describe the weakly bound electron of . A satisfactory agreement is obtained with the experimental cross section.

Transfer ionization in slow H++H- collisions

The transfer ionization reaction H-a(-) + H-b(+) = H-a(+) + H-b(1s) + e, on which we had previously carried out experiments and calculations, is reconsidered here at higher collision energies and interpreted as ionization of weakly bound electron of the H- ion, accompanied by a simultaneous resonant exchange of the 1s core electron. The ionization of H- is treated as being strongly coupled to the dominant mutual neutralization channels H-a(-) + H-b(+) = H-a (1s) + H-b (nlm), and the cross sections for all relevant reaction channels are calculated by using the molecular-orbital close-coupling scheme.

H(3s) Beam Production By Laser Excitation of Metastable Hydrogen-atoms in An Electric-field .2. Theoretical Approach

For pt.I see ibid., vol.18, no.18, p.3557-37 (1985). A quantitative description of H(3s) atoms produced by laser excitation of a metastable hydrogen beam in an electric field is performed and compared with the recent experimental results of Claeys et al. (1985). The Stark effect for n=3 is calculated to obtain the relative intensities of the five Stark transitions as a function of the field strength. Good agreement with the experimental values is found. The dynamical behaviour of the 3s and 3p Stark states when the atoms leave the field is then analysed. Due to the adiabatic evolution we found that only one Stark state can produce H(3s) atoms.

Electron detachment in H+-H- collisions

This letter reports a two-state model calculation of the cross section of the electron detachment reaction HA++HB- to HA++HB+e. Centre B is chosen as electron coordinate reference and the asymptotic parts of both the interaction and the energy difference are considered. Agreement with experiment entails the interpretation of the detachment process, as a dipole transition to the continuum under the Stark effect induced by the proton.

H(3s) Beam Production By Laser Excitation of Metastable Hydrogen-atoms in An Electric-field .1. Experiment

An experimental method to produce an intense fast beam of H(3s) atoms is described. H(3s) atoms are formed in a two-step process, first laser excitation of a beam of H(2s) atoms is achieved in an electric field where transitions occur between Stark states; in the second step, the atoms travel to a zero-field region and the Stark states formed evolve adiabatically to non-perturbed atomic states. By adjusting the laser frequency, 2s-3s excitation can be achieved. A neutral hydrogen beam with 2.7% of the atoms in the 3s state has been produced at an energy of 3 keV with 400 mW laser power.

Electron Loss From H(3p) Atoms in Collision With H-2-molecules and Rare-gas Atoms - Intense H(3p) Beam Production By Laser Excitation of Metastable Hydrogen

A method of producing an intense beam of H(3p) atoms is described. The 3p hydrogen atoms are formed by laser excitation of metastable H(2s) atoms and efficiencies of the order of 0.3 to 0.4 are easily obtained. The metastables themselves are formed by the charge exchange of protons in a Cs vapour. Cross sections for electron loss from H(3p) atoms and H(2s) atoms in collision with H2 molecules and rare-gas atoms have been measured in the energy range 1260-3600 eV in the forward direction (10 mrad acceptance). The results are normalised to absolute cross sections obtained by Roussel et al. (1977) for electron loss from ground-state hydrogen atoms in collision with the same targets. Comparison with other measurements is only possible for electron loss from H(2s) atoms and a good agreement with other authors is found.

Transfer ionization in H++H

Absolute cross sections for transfer ionization in H/sup +/+H/sup -/ collisions have been measured in the center-of-mass energy range 50 eV--40 keV, with the use of merged- and crossed-beam techniques, together with coincident detection of the products. A mechanism is proposed for the process in the low-energy region. The cross section, calculated accordingly, is found to be in satisfactory agreement with the experimental data.

Transfer ionization inH++H−collisions

Absolute cross sections for transfer ionization in H/sup +/+H/sup -/ collisions have been measured in the center-of-mass energy range 50 eV--40 keV, with the use of merged- and crossed-beam techniques, together with coincident detection of the products. A mechanism is proposed for the process in the low-energy region. The cross section, calculated accordingly, is found to be in satisfactory agreement with the experimental data.

Transfer ionization in H/sup +/+H/sup -/ collisions

Absolute cross sections for transfer ionization in H/sup +/+H/sup -/ collisions have been measured in the center-of-mass energy range 50 eV--40 keV, with the use of merged- and crossed-beam techniques, together with coincident detection of the products. A mechanism is proposed for the process in the low-energy region. The cross section, calculated accordingly, is found to be in satisfactory agreement with the experimental data.