The step-by-step experimental investigations of mechanisms of inter-related processes in electronic and atomic subsystems on UV-VIS. illuminated surface of wide bandgap oxides are presented. The variety of complementary experimental methods such as the mass-spectrometry, the optical and ESR spectroscopies, UV-photoelectron spectroscopy have been adapted to carry out in situ investigations in three phases: gas-adsorbate-surface. The origin of excitation of electron subsystem in the above-bandgap range as well as in the sub-bandgap range of photon energy is discussed. The nature of metastable state of photoexcited surface and the role of photodesorption and photoadsorption of oxygen in energy relaxation is treated. Using the time-of-flight spectroscopy the composition and the kinetic energy distributions of arising photodesorbed particles are analyzed. The dynamics of bond rearrangements and bond breaking is discussed in the framework of charge transfer approach in excited clusters. The potentialities of the presented results for probing and characterization of the electronic and atomic structure of active sites on the surface as well as for regulation of the number and composition of surface defects are discussed.