New grating experiments in the study of irreversible photochemical reactions

We have investigated the irreversible hydrogen abstraction of benzophenone in glassy polymers through holographic grating techniques. Recording the decay of the transient grating after pulsed excitation and the building up of a permanent grating during CW excitation allows the extraction of valuable information about the photochemical kinetics. Variation of the fringe spacing permits one to distinguish diffusive and reactive processes, and so transient grating experiments promise to be of great value in the study of diffusion-controlled reactions. As grating experiments are sensitive to changes in the absorption coefficient as well as the index of refraction, one can very sensitively detect density changes and deformations of the matrix which accompany the photochemical transformation in the sample.