H- FORMATION BY ELECTRON-CAPTURE IN HYDROGEN-AL(111) COLLISIONS - PERTURBATIVE AND NONPERTURBATIVE APPROACHES

H- formation in grazing H-Al(111) collisions is theoretically studied in the nonperturbative coupled angular mode (CAM) method. In this system, the charge transfer is a resonant one-electron process assisted by the collision velocity parallel to the surface. Nonperturbative CAM results are found to quantitatively agree with the experimental results of Wyputta et al. [Nucl. Instrum. Methods B 58 (1991) 379]. They are found to be quite different from standard perturbation results. The origin of the discrepancy is shown to lie in the neglect by the perturbation approach of the long range image potential in the e--surface interaction and a new set of perturbation results, taking this interaction into account, is presented; it is compared with the CAM results and shown to almost remove the discrepancies.