The somewhat lower transition state energy for the reaction with SiBr2 compared to SiCl2 implies that when etching occurs by formation of a chemisorbed SiX2 (X = H, Cl, or Br) from a chemisorbed Si atom, a brominated chemistry should allow for easier desorption of the SiX2 compared to a chlorinated chemistry, which can explain the somewhat higher etching rate observed for brominated chemistry.