Theoretical studies of slow collisions. Elastic electron scattering from positive ions, charge transfer in one-electron ion-ion systems and mutual neutralization of H-/D- and H2+

Quantal and semi-classical methods have been used to investigate slow electron, ionic and molecular collisions. Three distinct areas have been considered: the elastic scattering of electrons from positive ions, the symmetric resonance charge transfer in one-electron ion-ion collisions and the mutual neutralization of the hydrogen molecular ion and the negative hydrogen or deuterium ion. Differential cross sections for the elastic scattering of electrons from the closed-shell ions Na+, Cs+, Mg2+, N3+ and Ar8+ were obtained employing model and psuedopotential and quantum defect methods in a partial-wave analysis. Results were found to be consistent with recent experiments (Williams 1999 Rep. Prog. Phys. 62 1431) for Na+ and N3+, but less good agreement was obtained for Cs+ and Ar8+. The symmetric resonance charge transfer reaction AZ+ + A(Z-1)+ (1s) → A(Z-1)+ (1s) + AZ+ with Z > 1 has been investigated. In particular, differential cross sections for charge transfer in the 4He+-3He2+ system were determined in the perturbed stationary states approximation. These two-state semi-classical calculations were found to be in excellent agreement with fully quantal calculations of Falcon (1983 J. Phys. B: At. Mol. Phys. 16 1793), and in reasonable agreement with calculations and experiment of Kruedener et al (1997 Phys.Rev. Lett. 79 1002). Total cross sections for this and iso-electronic systems were found to agree with simple approximations. Total cross sections for the mutual neutralization reaction H2+ + D- → H2(1s, nl) + D(1s) + Δε were found using the Landau-Zener curve-crossing model. This method of calculation is heavily dependent on the reliability of estimates of the coupling matrix elements. Potential energy curves for the H2 molecule were found using the MOLPRO package in order to have a consistent base from which to determine the energetics of the reaction. Agreement with early experiments of Aberth et al (1971 AFCRL Report No. 71-0481 Bedford, Mass.) is satisfactory, but is less good with more recent experiments of Peart et al (1997 J.Phys.B: At.Mol.Phys. 30 4955) where there is some doubt over the adequacy of the detector acceptance angle. (author)