On the molecular effect in hydrogen molecular ions penetration through thin films

Penetration of low energy (2-12 key) hydrogen molecular ions (H-2(+)) and single protons through thin (40 angstrom) carbon films is simulated using molecular dynamic approach. It is shown that the width of energy loss spectra for the case of H-2(+) penetration is larger than that for H+ spectra (a "molecular effect") as it was previously observed in experiments [1]. This is explained by the molecular ions dissociation in the first few monolayers of the target. A simple semi-analytical model accounting for the molecular effect is provided. Results of simulations are compared with experiments. (C) 2012 Elsevier B.V. All rights reserved.