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Trajectory-dependent energy loss for swift He atoms axially scattered off a silver surface

Angle- and energy-loss- resolved distributions of helium atoms grazingly scattered from a Ag(110) surface along low indexed crystallographic directions are investigated considering impact energies in the few keV range. Final projectile distributions are evaluated within a semi-classical formalism that includes dissipative effects due to electron-hole excitations through a friction force. For mono-energetic beams impinging along the $[1\bar{1}0]$, $[1\bar{1}2]$ and $[1\bar{1}0]$ directions, the model predicts the presence of multiple peak structures in energy-loss spectra. Such structures provide detailed information about the trajectory-dependent energy loss. However, when the experimental dispersion of the incident beam is taken into account, these energy-loss peaks are completely washed out, giving rise to a smooth energy-loss distribution, in fairly good agreement with available experimental data.