Study of atomic excitation in sputtering as a function of the projectile incidence angle

Solid targets of elemental beryllium, boron, magnesium, and gold have been bombarded with 80-keV ${\mathrm{Ar}}^{+}$ ions. Intensities of photons emitted from sputtered particles have been measured as functions of the angle of incidence of the projectile. Generally, the excitation intensities increase with increasing angle of incidence, but a few levels show much stronger angular variations than the majority of levels do. The results are discussed. It is concluded that whereas the common increase in excitation is caused by the general increase in the number of swift, sputtered atoms, a few levels are in addition selectively excited through molecular-orbital electron-promotion processes taking place in binary collisions.