Electronic Mechanisms in Solid-State Photolysis

Abstract

When some crystalline solids are photolytically decomposed several of the effects which occur indicate that electrons, holes, or excitons are involved in the reaction. In addition the kinetics of many of these reactions appear to be approximately, but not precisely, second order. The nature of these effects suggests that the photolytic reactions are essentially electronic and that they occur at certain crystal sites or defects when these become doubly excited. The results obtained when NaBrO₃ is photolytically decomposed, particularly the dependence of the equilibrium rate on light intensity, suggest that the doubly excited sites may also generate additional sites. Furthermore, the data indicates that some decomposition sites may be generated from precursors that are expended during the photolytic reaction. Using these concepts a phenomenological theory has been developed which is consistent with current results. In particular it indicates that the photolytic rate vs. time curves should be resolvable into one constant and two exponential components. It also predicts, in agreement with the data, that the exponential component attributable to the sites generated from precursors should be reduced— even to the point of disappearing—when the material is subjected to ionizing radiation prior to photolysis.

Research performed promarily at Brookhaven National Laboratory and supported by Picatinny Arsenal and the U. S. Atomic Energy Commission.