The interaction of UV-VIS irradiated oxide surface with gaseous oxygen has been studied. The investigations in three phases, gas-adsorbate-surface, have been carried out by means of complementary experimental methods, such as photo-mass-spectrometry, optical, ESR, UPS and "time-of-flight" spectroscopies. The solid oxide surface was photoactivated in both the above-bandgap and sub-bandgap regions under low and high intensities from 10^-3 up to 10⁸ W/cm². The experimental results suggest a 3-step model: (i) a fast initial single-particle-like electronic excitation of oxide, (ii) a charge transfer, (iii) chemical bonds' breaking and formation resulting in atomic rearrangements on the surface. The oxygen photodesorption, photoadsorption and activation are governed by electron transitions and can be treated in the framework of the Menzel-Gomer-Redhead model. Molecular processes play an important role as a compet-Rive channel in the surface electronic deexcitation. The potentialities of "photoactivation spectroscopy" for surface probing and preparation are discussed.