Importance of considering helium excited states in He + scattering by an aluminum surface

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

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

American Physical Society

Año: 2014 vol. 90 p. 1954161 - 19541610

0163-1829

The He+/Al system is a very interesting projectile-surface combination which was thought initially as anexample of a pure Auger neutralization mechanism. Then, because of the measured reionization explained bythe antibonding interaction of the projectile state with the core target states, the resonant charge exchangewith the band states was considered as another important contribution to the neutralization. Nevertheless, byonly considering the neutralization to the ground state of helium, the measured ion survival probability is stilloverestimated. On the other hand, measurements of electron emission from an Al surface bombarded by Hepositive ions suggested the possibility of occupied excited states of helium due to the ion-surface collision.In this work, we also include the excited states of He within the time-dependent scattering process in whichboth neutralization mechanisms, resonant and Auger, are simultaneously contemplated. Our starting point is amultiorbitalAnderson Hamiltonian projected over the selected space of ground and excited atomic configurations.An extra term related to the Auger mechanism is added to this Hamiltonian. A difference with previous works isthat this approach includes the electron spin and, therefore, the spin fluctuation statistics in the charge-exchangeprocess is correctly taken into account. We find a notable improvement in the agreement with the experimentsand also that the interference between both mechanisms is not dramatic