XeF2 was reacted with silicon, and the gaseous products were detected using modulation techniques which made the experiments sensitive only to products which had not collided with a wall. In agreement with previous experiments, SiF4 was found to be the major reaction product. Radicals such as SiF and SiF2 were observed at a much lower level. However, SiF2 was not found to be the dominant species as might have been suspected on the basis of experiments by other workers with atomic fluorine. Bombardment with 2000-eV argon ions enhanced the rate of product formation and decreased the fraction of the products that was SiF4. Production of radical species, in particular SiF2, was enhanced. Collisions of SiF2 with fluorinated, stainless-steel vacuum chamber walls were investigated in order to determine whether the SiF2 radical was converted to SiF4 as suggested by others. Wall reactions were found to be important in some circumstances and not important in others.