Product selectivity and yields of cyclohexanol and cyclohexanone formation in the photocatalytic air oxidation of cyclohexane on TiO2 particles were determined as a function of the irradiation wavelength (254 less than or equal to lambda/nm less than or equal to 366) and the photon flux (0.3 less than or equal to I-0/neinstein cm(-1) s(-1) less than or equal to 5.0). Photonic efficiencies for total monooxygenated products (cyclohexanol + cyclohexanone) ranged from 10 to 25% depending on photon energy and fluency. The cyclohexanol-to-cyclohexanone ratio linearly increases with the incident photon flux at each wavelength and varies more than a magnitude order-from 3 to 32%-at the same incident photon fluency-5 neinstein cm(-2) s(-1)-by changing the irradiation wavelength from 366 to 303 nm. Experimental evidence indicates that both spectral and intensity effects emerge as a consequence of the change in the frequency of photon absorption per particle. A mechanism is proposed which accounts for the origin of the selectivity changes.