This paper reports the use of a modulated ion beam system to probe the reaction dynamics occurring in an ion/surface interaction which results in the removal of material from a solid. A modulated ion gun (15 μs rise time) was used to provide pulses of incident ions (primarily CF+3) at a Si surface. The resulting products were detected by a mass spectrometer and signals have been observed at mass 28 (Si), mass 47 (SiF), mass 66 (SiF2), and mass 85 (SiF3, principal cracking fraction of SiF4). A comparison of the amount of signal with the measured cracking pattern of SiF4indicated that a substantial fraction of the Si left the surface with fewer than four fluorine atoms. By performing the experiments in two different sample positions, we have confirmed that complications due to collisions between the product molecules and the vacuum system walls have been eliminated. The time evolution of these product signals following the start of the ion beam pulse has been measured with signal averaging. The results are consistent with a model where mass 47 (SiF) and mass 66 (SiF2) are produced with ∼1 eV energy in a fast process. Roughly 70% of the Si is removed in this manner. In contrast, mass 28 (Si) and mass 85 (SiF3and SiF4cracking fraction) have an appreciably slower time dependence and a model which partially fits this observation assumes that these species are produced at the same time as SiF and SiF2but have thermal (0.02 eV) energies and thus take longer to reach the mass spectrometer. The observed time dependence is even slower than this model predicts, however, which indicates the possibility of a surface residence time delay due to the formation of a surface complex prior to the desorption of the products.