HYDROGENATION OF THE SILANONE GROUPS (SI-O)(2)SI=O - EXPERIMENTAL ANDQUANTUM-CHEMICAL STUDIES

The reactivity of bis(siloxy)silanone groups (=Si-O)(2)Si=O stabilized on a silica surface with respect to H-2 molecules was studied. The re action was found to give the (=Si-O)(2)SiH(OH) groups. The rate consta nt for this process was determined. Its activation energy in the 300-5 80 K temperature range is 13.4+/-0.3 kcal mol(-1), and the enthalpy is 54+/-5 kcal mol(-1). The activation energy for the reverse reaction, viz., elimination of a hydrogen molecule, is equal to similar to 65 kc al mol(-1). Quantum-chemical calculations of hydrogenation of F2Si=O a nd (HO)(2)Si=O, which are the simplest molecular models of the silanon e groups, were performed. Data on the geometrical and electronic struc tures of transition states and on the effects of substituents at the s ilicon atom on the reactivity of the silanone groups in this process w ere obtained. The optical absorption band of the surface silanone grou ps was quantitatively characterized. Its maximum is located at 5.65+/- 0.1 eV; the extinction coefficient at the maximum epsilon(220 nm) is ( 3+/-0.5). 10(-18) cm(2) molec.(-1).