Interaction of gas-phase atomic chlorine with a silicon surface: Reactions on bare and hydrogen-chemisorbed surface sites

The reaction of gas-phase atomic chlorine with hydrogen atoms chemisorbed on a silicon surface is studied by use of the classical trajectory approach. In the model the gas atom interacts with the preadsorbed hydrogen atom and adjacent bare surface sites. The reaction zone atoms are configured to interact with a finite number of primary-system silicon atoms, which are coupled to the heat bath. The study shows that the chemisorption of Cl(g) is of major importance. Nearly all of the chemisorption events accompany the desorption of H(ad), i.e., a displacement reaction. Although it is much less important than the displacement reaction, the formation of HCl(g) is the second most significant reaction pathway. At a gas temperature of 1500 K and surface temperature 300 K, the probabilities of these two reactions are 0.829 and 0.082, respectively. The chemisorption of Cl(g) without dissociating H(ad) and collision-induced dissociation of H(ad) are found to be negligible. In the reaction pathway forming HCl, most of the reaction energy is carried by HCl(g). The ensemble-averaged vibrational, rotational, and translational energies are 37.4%, 35.6%, 18.3% of the liberated energy, respectively. Less than 9% of the energy dissipates into the solid phase. Although the majority of HCl produced in the gas phase belongs to a fast component of the time-of-flight distribution for a direct-mode reaction, there is a significant amount of HCl belonging to a slow component, which is characteristic of complex-mode collisions. (C) 1999 American Institute of Physics. [S0021-9606(99)71045-7].