We report a detailed photoacoustic study of a highly exothermic solidhyphen;state reaction, the photopolymerization of diacetylene crystals. Both the amplitude and the phase shift of the photoacoustic signal are monitored during the course of the polymerization at various UV excitation wavelengths and various chopping frequencies. A onehyphen;dimensional heathyphen;diffusion model employing impedance boundary conditions is shown to fit the experimental data quite adequately. We conclude from the theoretical interpretation of the results that the quantum yield for photopolymerization is very high (sim;100) and that the polymer acoustically couples much more effectively to the gas than does the monomer.
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