Modulated beam mass spectrometry has been used to investigate the etch products, surface chemistry, and product desorption mechanisms for the interaction of XeF2 with W(lll). Spontaneous etching was found to be very slow at room temperature but was enhanced substantially by bombardment with argon ions. It will be shown that ion bombardment causes the reaction probability (sticking probability) of XeF2 to increase from quite small values to almost unity. The desorbed etch product is primarily WF6 (gas). It will be shown that three factors influence ion enhanced chemistry for the W(11 l)-XeF2 system. First, ion bombardment causes tungsten and fluorine, which coexist in a stable form on the surface, to react chemically with each other to form WF6 (gas). WF6 physically trapped in the lattice may also be desorbed by ion bombardment. Secondly, ion bombardment produces lattice damage which enhances the spontaneous reaction between XeF2 and W(111). Finally, ion bombardment also tends to suppress the etch rate under some conditions. The first mechanisms seem to dominate the etching reaction except at low XeF2 fluxes. This paper will emphasize the interpretation of these observations. © 1985, American Vacuum Society. All rights reserved.