Vicinage effects in the stopping power of H3+ beams in amorphous carbon

The stopping power of H3+ molecular beams incident on amorphous carbon foils is analyzed as a function of the orientation of the molecule relative to its direction of motion. The electronic stopping power was calculated within the dielectric formalism, taking into account the dynamics of the Coulomb repulsion among the molecular partners. At intermediate velocities, v 2 a.u., the stopping ratio for the perpendicular orientation is greater than for the parallel one, while the opposite behaviour is shown for higher velocities. The stopping ratio for randomly oriented H3+ molecules was evaluated for different target thicknesses, resulting in larger values for the thinner targets and the higher energies. Comparison of our results with available experimental data shows a reasonable agreement.This work was supported in part by the Spanish Dirección General de Investigación Científica y Técnica (projects PB93-1125 and PB95-0689). CDD thanks the Instituto de Cooperación Iberoamericana for a doctoral fellowship. NRA wishes to thank the Conselleria d’Educació i Ciència de la Generalitat Valenciana for a visiting professor fellowship to the Universitat d’Alacant under the program PROPIO