There are many examples of situations in which a gas-surface reaction rate is increased when the surface is simultaneously subjected to energetic particle bombardment. There are several possible mechanisms which could be involved in this radiation-enhanced gas-surface chemistry. In this study, the reaction rate of silicon, as determined from the etch yield, is measured during irradiation of the Si surface with 1 keV He+, Ne+, and Ar+ ions while the surface is simultaneously subjected to fluxes of XeF2 or Cl2 molecules. Etch yields as high as 25 Si atoms/ion are observed for XeF2 and Ar+ on Si. A discussion is presented of the extent to which these results clarify the mechanisms responsible for ion-enhanced gas-surface chemistry. © 1981.