The interaction of a series of molecular probes (O-3, H2S, CO, NH3, (CH3)(2)CO, C5H5N and CH3CN) with the hydrated SiO2, surface has been investigated by QM/MM calculations and diffuse reflectance infrared Fourier transform spectroscopy. Theoretical estimates of O-H stretchings are shown to be improved by a new treatment of the molecular mechanics part of the model. Such a result is encouraging for the application of the adopted approach to other systems. (c) 2005 Elsevier B.V. All rights reserved.