We present results of molecular dynamics simulations of reactive ion etching (RIE) of a reconstructed Si(100)(2x1) surface. The existing Stillinger-Weber interatomic potential for Si/Cl of Fell ed al. has been modified by correcting the Si-Si bond strength for a SiCln moiety bound to a Si surface and the Si-Cl bond strength in SiClm molecules. This potential has been used to study RTE of Si by Gland Cl-2 ions. The calculated properties such as the Si yield, product stoichiometry, stoichiometry of the chlorosilyl surface, and Cl content of the chlorosilyl layer are in reasonable agreement with experiment. The dissociative chemisorption probability of Cl-2 on Si(100)(2X1) as a function of energy has been simulated and the results are in reasonable agreement with experiment.