A new model optical potential for Ps formation in positron scattering from H and He

Abstract

PACS. 34.10+x -General theories and models of atomic and molecular collisions and interactions (including statistical theories, transition state, stochastic and trajectory models, etc.). PACS. 34.90+q -Other topics in atomic and molecular collision processes and interactions. PACS. 34.50Lf -Chemical reactions, energy disposal, and angular distribution, as studied by atomic and molecular beams.

Positron annihilation in CO 2 molecules: The role of vibrational excitation

“…( 13) if any meaningful comparison with experiments has to be made. We have extensively discussed before [17,18] positron scattering from atoms and molecules and we will therefore not be repeating here the details of our methods. Suffice it to say that we employ a Single-Center-Expansion (SCE) of both the interaction (13) and of the wave function (7) and that we obtain the v λ st from exact molecular multipoles, while the v pcop λ contributions come from a Density Functional treatment of short-range correlation [19] which is then smoothly connected with the long-range dipole polarisability of the target molecule [17,18].…”

“…We have extensively discussed before [17,18] positron scattering from atoms and molecules and we will therefore not be repeating here the details of our methods. Suffice it to say that we employ a Single-Center-Expansion (SCE) of both the interaction (13) and of the wave function (7) and that we obtain the v λ st from exact molecular multipoles, while the v pcop λ contributions come from a Density Functional treatment of short-range correlation [19] which is then smoothly connected with the long-range dipole polarisability of the target molecule [17,18]. Such an approach has been tested before in our studies and found to be quite successful in describing the low-energy behaviour of elastic cross-sections, integral and differential [20,15,21] for the dynamics of positron collisions from molecular targets.…”

Positronium formation with ionic targets: an optical potential calculation

“…in order to analyse the capabilities of a theoretical model based on the extension of the optical potential which has been successfully used in analysing analogous charge-exchange collisions with neutral targets (Gianturco and Melissa 1996a). In the present work we construct the absorption part of the optical potential by using an integral relation which connects it to the polarization potential.…”

“…Since the asymptotic wavefunction is made explicitly antisymmetric, the cross sections can be calculated without the additional difficulty of modelling the exchange forces. The calculation procedures adopted here follow the same scheme previously used when studying positronium formation with neutral targets (Gianturco and Melissa 1996a). We will give in this work only a brief account of the main theoretical aspects of the model, since a more detailed discussion on this subject has been recently published by the same authors (Gianturco and Melissa 1996b).…”