| Density functional theory of electronic structure has been applied to predict interactions of adsorbates on two solid surfaces, the Si (100)-(2 x 1) surface and the ice Ih surface. Although some features of the mechanism for the decomposition of silane on Si (100)-(2 x 1) are known from experiment, the microscopic picture of this decomposition is unclear. In this work, the relative energetics of fragments of silane adsorbed onto the Si (100)-(2 x 1) surface are investigated. The lowest energy structure for silyl and hydrogen fragments adsorbed onto the surface is found to have the fragments added to opposite sides of a silicon surface dimer. This structure is metastable with respect to a silicon dihydride bridging the surface dimer. A microscopic picture of surface decomposition is discussed. Silane has a small probability of sticking to the Si (100)-(2 x 1) surface (10{dollar}sp{lcub}-5{rcub}){dollar} but the activation barrier due to surface heating is small (0-5 kcal/mol). In this work, two mechanisms for dissociative adsorption of silane onto Si (100)-(2 x 1) are found. Both mechanisms require excitation of silane degrees of freedom to reach the transition state, and both mechanisms have energy barriers consistent with a small sticking probability. Tilting of the surface dimer plays an important role in these mechanisms. Heterogeneous reactions involving HOCl on ice may play a significant role in ozone destruction in the stratosphere. The adsorption energy for HOCl on ice is stronger than that of a typical hydrogen bond. In this work, the strength of binding of HOCl on ice is shown to be due the hydrogen bond formed with the binding site water, as well as electrostatic and polarization interactions with other water molecules of the ice surface. It is determined that HOCl will preferentially bind by donating a proton to a surface water molecule. The influence of proton order, cluster size, surface relaxation, and surface structure on modeling the interaction of HOCl on ice are investigated. Among these factors, surface structure is found to be the most significant in altering binding. |
