ELECTRONIC EXCITATION OF H-2 BY POSITRON-IMPACT - AN APPLICATION OF THE SCHWINGER MULTICHANNEL METHOD

In this paper we report integral and differential cross sections for positron-impact excitation of the X 1SIGMA(g)+ --> B 1SIGMA(u)+ transition in H-2 for collision energies of 13.5, 15, 17.5, 20, 25 and 30 eV. These cross sections were derived from fixed-nuclei scattering amplitudes in such a way that low angular-momentum components are obtained using the Schwinger multichannel method and the large ones are treated by the first Born approximation. To our knowledge, up to date no experimental data are available for comparison. Our results differ from previous theoretical results of Mukherjee and co-workers. We discuss possible reasons for this disagreement.2791881188

Elastic cross sections and annihilation parameter for e(+)-H-2 scattering using the Schwinger multichannel method

We report detailed results for positron-H-2 collisions obtained with the Schwinger multichannel method. Our calculations include annihilation parameter, differential, integral, and momentum transfer cross sections for energies below the positronium formation threshold. The calculations were carried out in the static-plus-polarization approximation with symmetry-resolved cross sections. Energy (temperature) dependence and symmetry-resolved contributions for the annihilation parameter Z(eff) are also reported. Our ab initio integral cross sections are found to be in good agreement with the experimental data. [S1050-2947(98)04409-6].5853502350

Superelastic collisions of electrons with the c(3)Pi(u) metastable state in hydrogen dc positive column

We investigated the effect of superelastic electronic collisions of electrons, with the c (3)Pi(u) state of the H-2 molecule, on the electron energy distribution function (eedf) of a de positive column. We use a recently calculated set of electronic superelastic collision cross-sections [C.S. Sartori, F.J. da Paixao, M.A.P. Lima, Phys. Rev. A 55 (1997) 3243] to study the effect of these collisions on the eedf, the transport parameters, ionization and dissociation rates. We include two possible pathways, c (3)Pi(u) --> b (3)Sigma(u)(+) and c (3)Pi(u) --> X (1)Sigma(g)(+), for superelastic collisions of electrons with molecules in the metastable state. Cross-sections of the order of 10(-14) cm(2) at low energy enhance the eedf tail by superelastic electronic collisions, in particular for low reduced electric field E/N. This result changes considerably the dissociation and ionization rates by six orders of magnitude in the region from 10 to 50 Td. (C) 1999 Elsevier Science B.V. All rights reserved.2464169927528