This paper comments on the results of recent studies of Ar + scattering on Mg, as well as Al and Si, surfaces by Blum et al and Nixon et al . The strong excitation of Ar * * 3p 4 4s 2 states is reported in these works, especially for low (1 keV) collision energies. This result contradicts our earlier work and the work of other authors. We re-investigated Ar + scattering but did not find any evidence of Ar * * state production. However, Ar * * state production is observed in Ar ++ collisions and we conclude that a contamination of the Ar + beam with Ar ++ in the work of the above authors is responsible for their observations. We also comment on the identification of structures due to excited sputtered Mg.