Proton-induced kinetic plasmon excitation in Al and Mg

We report energy distributions of electrons emitted from Al and Mg surfaces bombarded by 3-100-keV/amu hydrogen and deuterium ions. The energy spectra contain structure consistent with the decay of bulk plasmons, even below t he velocity threshold expected from current theories. To explain the result s we compare the importance of additional mechanisms involving electron cap ture, lattice-assisted excitation, and excitation by fast secondary electro ns.