A local density functional investigation was made of the adsorption geometry and the surface diffusion activation energies of hydroxyl (OH) radicals that resulted from dissociative water adsorption on Si(100)-2 x 1 surfaces. In a similar manner to atomic H, the OH preferred to bind to a single surface Si atom. Due to both dative interactions with surface dangling bonds, and to adsorbate-adsorbate H bond-like interactions, the O-H bonds tended to be oriented perpendicularly to the dimer direction. This was in agreement with electron stimulated desorption ion angular distribution data. The energetics of OH diffusion on clean or saturated surfaces were similar to that of H, but with slightly lower barriers. In particular, the intra-dimer barrier was found to be about 0.2eV lower. This implied that room-temperature intra-dimer adsorbate oscillations should occur some 1000 times faster for OH. The absolute value of this barrier (0.9eV) was in accord with scanning tunnelling microscopic observations.

A.Vittadini, A.Selloni, M.Casarin: Physical Review B, 1995, 52[8], 5885-9