Comparison of one and two centre studies of low energy scattering by diatomic molecules

Polarisation potentials for positron-molecule collisions: positron-H2scattering

“…However, there is some indication of such a structure (at about 3.8 eV) in the results of Charlton et a1 (1980,1983). The theoretical cross sections of Lodge et al (1971), Baille et a1 (1974), Hara (1974) and Sur and Ghosh (1982), all of which were based on electron-H2 polarisation potentials, exhibit a minimum in the total cross section, although the energy at which this minimum occurs and the rapidity of the decrease of U,,, with increasing energy differ significantly among these results.…”

Angular correlation of two-photon positron annihilation in hydrogen gas

“…(The low energy annihilation considered here involves a close positron-electron encounter and an accurate wave function would reflect this through a n explicit, positronium-like, dependence on the electron-positron coordinate (ri -x). Clearly the present wave function [3] does not possess this property.) In light of this the rather good agreement between the calculated and measured angular distributions is somewhat surprising.…”

“…The scattering of low energy positrons by molecular hydrogen has been recently investigated theoretically (see, for example, Baille et al (1, 2), Darewych et al (3), Hara (4) and papers cited therein) and experimentally (5,6). The theoretical investigations have involved the calculation of the low energy elastic, momentum transfer, rotational and vibrational excitation cross sections as well as the annihilation rate, using a simple one-state approximation in which only the electrostatic potential and the adiabatic distortion potential of the H, molecule are taken into account, whereas the vibrational and rotational excitations are calculated using the adiabatic-nuclei approximation (see, for example, the review article by Golden et al (7)).…”

Rotational excitation of N2 by positron impact in the adiabatic rotational approximation

“…As far as we know, direct measurements of positron-N 2 rotational cross sections are not available until today. Nonetheless, the theme has attracted the attention of theorists [19][20][21] since the 70s and, from time to time, improved calculations were reported in literature. Of direct interest to us here are the cross sections reported by Mukherjee et al [22], del Valle and Gianturco [5] and Mukherjee and Mukherjee [23].…”