Role of He excited configurations in the neutralization of He+ ions colliding with a HOPG surface

A. IGLESIAS GARCÍA; EVELINA A. GARCÍA; E. C. GOLDBERG

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Lugar: New York; Año: 2013 vol. 87 p. 754341 - 7543413

0163-1829

The very high neutral fractions measured in He+ scattered by graphitelike surfaces, at intermediate incomingenergies (1 keV < Ein < 6 keV), cannot be explained only by the resonance of the He ionization level withthe valence band states of the surface. Excited configurations (1s2s) and (1s2p) appear as possible resonantneutralization channels together with the ground state one (1s2). We develop, in this work, a time-dependentquantum-mechanical calculation of the charge-transfer process in He+/HOPG collision, where the resonantneutralization to the ground and first excited states of He is taken into account.We use an Anderson Hamiltonianprojected on the electronic configurations of the projectile atom which are energetically favorable for thecharge-exchange process. Thus, an exhaustive analysis of different possible approximations to the neutralizationof He+ is performed: the typical neutralization to the ground state by either neglecting or not the electron spin andfinally the one including excited configurations.Our results reproduce the observed experimental trends onlywhenexcited configurations (1s2s) and (1s2p) are involved in the charge exchange between the ion and the surface.