2-Propanol oxidation to acetone was examined by time-resolved infrared spectroscopy on a Pt/TiO2 photocatalyst in an aqueous solution. Holes generated by the band-gap excitation were found to attach to the adsorbed reactant within the first 0.5 mus. Subsequent rearrangement of atoms in the hole-attached reactant was observed on a series of time-resolved vibrational spectra. The C=O stretching band of a reaction intermediate to be converted to acetone appeared at time delays of 0-20 mus. The observed wavenumber of the intermediate, 1640 cm(-1), was compared with theoretically predicted C=O stretching frequencies of possible species. An acceptable agreement was obtained with the anion radical of acetone adsorbed on the catalyst. (C) 2003 Elsevier B.V. All rights reserved.