Theoretical molecular orbital study of silanol-water interactions

Molecular modeling of silanol (adsorbent)-water (adsorbate) interactions by ab initio molecular orbital calculations provides relative interaction energies for different structures and induced bond length and angle changes. The initial adsorption of a single water molecule onto an isolated surface silanol will favor the H₂O proton acceptor structure, as compared with the H₂O proton donor structure. For the former, the SiO bond is shortened (strengthened), whereas for the latter, it is lengthened (weakened). For the combined adsorption of both water molecules, a significant water-water interaction occurs, suggesting that a gas-phase dimer can adsorb on an isolated silanol without the dimer separating completely.