Positron-impact electronic excitations and mass stopping power of H2

Abstract

Positron-impact electronic excitation cross sections, mean excitation energies and mass stopping power of the H2 molecule have been calculated for energies from 10 eV up to 2 keV using the convergent close-coupling method that utilizes single and two-center expansions. Results are compared to previous studies. Application of Bragg's rule of stopping power additivity is discussed by comparing results obtained for atomic (H) and molecular (H2) targets for positron impact.

Calculations of positron scattering on the hydrogen molecular ion

“…This is expected as positrons have been observed to lose their energy faster than electrons in a variety of different target materials [45]. A similar behaviour is seen in the CCC results for H 2 [28]. This difference is a consequence of the Barkas effect [46] which results from excitation and polarisation of bound electrons in a target by a projectile [47].…”

“…The most consistent approach to positron collisions with atoms and molecules is a two-centre close-coupling method where the total wave function of the collision system is expanded in the set of states from both the target and Ps centres. Within the CCC method the two-centre approach has been applied to positron scattering from atoms [26] and H 2 [27,28]. However, the two-centre approach is computationally demanding and relatively complicated to implement, particularly for charged targets [29,30].…”