Vicinage forces between molecular and atomic fragments dissociated from small hydrogen clusters and their effects on energy distributions

In this paper we analyze the dynamic evolution of molecular and atomic fragments of small hydrogen clusters interacting with thin solid foils. We compare the vicinage forces, calculated within the dielectric formalism, for H⁺, H⁰, and H₂⁺ fragments. Using a molecular dynamics numerical code we determine the energy distribution of the fragments after interacting with the target. This distribution is compared to experimental results for protons coming from the fragmentation of v=2.02a.u. H₂⁺ ions impinging on an aluminum foil; a fraction of neutral H⁰ is needed to be included in the simulation to get a good agreement with the experimental results. The H₂⁺ energy spectra for v=5.42a.u. H₃⁺ interacting with amorphous carbon is also determined. The asymmetry in the Coulomb peaks appearing in the energy spectra both experimentally and in our calculation is opposite for H₂⁺ than in H⁺; kinematic effects and differences in the electronic stopping are enough to reproduce the difference in the alignment of H₂⁺ and H⁺ fragments.