Formation of negative hydrogen ion in Positronium - Hydrogen collisions

TL;DR

This study theoretically investigates how excited states of Positronium influence the formation of negative hydrogen ions during collisions with hydrogen, highlighting the importance of higher order effects across a wide energy range.

Contribution

It introduces a Coulomb Modified Eikonal Approximation model that accounts for higher order effects, providing more accurate cross section calculations than the First Born Approximation.

Findings

Excited states of Ps significantly enhance H^- formation at low energies.

Higher order effects are crucial for accurate cross section predictions.

Differential cross sections show a double peak at high energies, absent in simpler models.

Abstract

The importance of the excited states of Positronium (Ps) in the formation cross sections(both differential and total) of the negative hydrogen ion (H^-) are investigated theoretically for the charge transfer reaction, Ps (n = 1, 2) + H --> e+ + H^- for a wide range of incident energies (e. g., threshold - 500 eV) . The calculations are performed in the frame work of a qualitative model, the post collisional Coulomb Modified Eikonal Approximation (CMEA) . A comparative study is also made between the capture from ground and excited states of the Ps. The present CMEA model takes account of higher order effects which is essential for a rearrangement process where the First Born type Approximation (Coulomb Born for the ionic case) is not supposed to be adequate. At low incident energies, the excited states of Ps (2s, 2p) are found to play a dominant role in the H^- formation cross sections . Significant deviations are noted between the present CMEA and the Coulomb Born (CBA) results even at very high incident energies (e.g., Ei = 500 eV), indicating the importance of higher order effects. At high incident energies the present CMEA differential cross section (DCS) exhibits a double peak structure which is totally absent in the CBA and could again be attributed to higher order effects.