X-RAY-EMISSION FOR 3-137 KEV AR17+ IMPACTING SIO2

We report X-ray spectra from Ar17+ impacting a SiO2 surface at 30 degr ees from normal incidence, for projectile energies ranging from 3 to 1 37 keV. At the highest energy we see only X-rays from the filling of t he argon K shell. As the projectile energy is reduced, these argon X-r ays are gradually reduced to zero while a silicon K-alpha peak appears . We interpret these data to be the result of the onset of a direct tr ansfer of a silicon K-shell electron to the K-shell vacancy in the arg on projectile. We suggest that this transfer occurs through an argon-s ilicon Auger process which takes place during a close collision in the solid. The velocity dependence of this process is not yet fully under stood.