The interaction of a hydroxyl radical with cluster models of a hydroxylated or-quartz surface was studied by means of density functional calculations. Two molecular models representing isolated (drop Si-OH) and geminal (=Si(OH)(2)) silanol-terminated quartz surfaces were used. Two reactive sites of the silanol models were investigated: the hydrogen of the silanol group and the surface-approximating, silicon atom. The (OH)-O-. binds weakly to the silanol hydrogen atoms in both models, with a reaction energy of about -7 kcal/mol. The silicon atom in the isolated silanol cluster is not reactive toward the (OH)-O-.. In contrast, the (OH)-O-. adsorbs on the Si in the geminal silanol cluster with a reaction energy of -4 kcal/mol. The Si-OSi bond in the resulting pentacoordinated silicon complex is weakened upon the (OH)-O-. adsorption and can be dissociated. The energy barrier to the dissociation is 4 kcal/mol, and the overall reaction energy is -4 kcal/mol. The dissociation of the Si-OSiH3 bond which mimics the Si-O subsurface bonding in the real quartz surface suggests a possibility of (OH)-O-. activated quartz surface layer disintegration. The calculated energy barrier in this (OH)-O-. radical activated process is significantly lower than the predicted energy barrier in the rate determining step in the OH- catalyzed quartz surface dissolution (19 kcal/mol). The Si-OSi bond rupture followed by formation of a Si-O-. radical on the surface may provide a plausible mechanism for reactivation of chemically inert, silanol terminated, aged quartz surfaces.