Photons absorbed by nanocrystalline TiO2 particles at 254 nm are found to be 7.7 times more efficient than those at 366 nm for driving the photocatalytic oxidation of salicylate S in aerated aqueous sols. The occurrence of this phenomenon is ascribed to the conjunction of (1) short diffusion times of photogenerated carriers to the surface of nanoparticles, a fact that allows chemical reaction to compete with energy relaxation, and (2) favorable donor E-0(S-/S-.) redox potential and interfacial reorganization energy lambda(R) values, which make electron-transfer rates peak at energies inside the valence band of TiO2. Master equation kinetic modeling shows that electron transfer from S into hyperthermal valence band holes takes place at rates consistent with k(sc) similar to 10(4) cm s(-1) at optimal exoergicity, if the excess energy is dissipated into the crystal lattice within a few picoseconds. Hydroxyl ions as donors would require much slower thermalization rates.