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Effects of projectile track charging on the H<sup>-</sup> secondary ion velocity distribution

Abstract:

The bombardment of insulating targets by MeV projectiles produces a positive track delivering secondary electrons to the solid. These electrons are eventually captured by adsorbed hydrogen-containing molecules, inducing fragmentation and initiating the H- secondary ion emission. The dynamics of this process is very sensitive to the track electric field and depends on the emission site and on the H- initial velocity. In this work, a model, based on a time-depending track potential followed by secondary electron induced desorption - SEID, is employed to describe the production and dynamics of H- secondary ion emission. It is shown that depending on how fast the track neutralization occurs, the movement of H- ions may be accelerated, decelerated or even aborted. Trajectories, angular distributions and energy distributions are pbkp_redicted and compared with experimental data obtained for water ice bombarded by 1.7 MeV nitrogen ions. © 2006 Elsevier B.V. All rights reserved.