Excitation of electrons from an Al surface by grazing-angle-incident fast heavy ions

Measurements were made, at various emission angles, of energy spectra of electrons from Al induced by grazing-angle-incident ions of ${\mathrm{N}}^{6+}$, ${\mathrm{Ar}}^{12+}$, and ${\mathrm{Xe}}^{27+}$ with equal velocities corresponding to 0.98 MeV/amu. A new line which could not be explained by any of the hitherto identified mechanisms was observed at an energy obviously larger than that of an electron with a velocity equal to the projectile. The projectile and emission angle dependencies of the line are consistent with the dynamic image potential acceleration mechanism.