Photoprocesses on a surface of nanoporous quartz under resonant laser radiation

Abstract

The photoexcitation of iodine molecules on surfaces of solid (nonporous) and nanoporous quartz by resonant laser radiation in the visible region has been studied. We have detected and studied the high-energy photodesorption of iodine molecules with a translational energy of 1.4 to 1.8 eV from nanoporous quartz surfaces at an exciting photon energy ranging between 1.9 and 2.3 eV, as well as the nonequilibrium surface dissociation of molecules. Unlike the photoprocesses, which are observed only on the surface of nanoporous quartz, the thermal desorption of I₂ molecules with a considerably lower kinetic energy has also been detected on the surface of solid quartz. We have suggested a physical mechanism of photodesorption, under which electronic excitation of an iodine molecule in the confined volume of a nanopore is accompanied by a Franck-Condon electronic transition of a molecule-surface complex to a state with a higher potential energy and subsequent release of this energy in the form of kinetic energy. It has been concluded that photoprocesses on a nanostructured surface are radically different from ordinary surface photoprocesses.