Infrared Studies of Long-Range Stress in Solid-State Peroxide Photoreactions

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Abstract
When crystals of di(undecanoyl) peroxide are photolyzed at low temperature to conversions greater than about 0.06%, in situ FTIR spectroscopy of the CO2 product shows numerous v3 bands which are not observed after less extensive photolysis. The shift of these bands to high frequency suggests the influence of stress fields generated by distant reaction sites. The influence becomes more pronounced upon annealing to about 140K, but disappears after annealing above 280K. This behavior is discussed in terms of relaxation through both rapid elastic deformation and stepwise, thermally activated plastic deformation. Isotope labeling shows that the new CO2 vibrations are not tightly coupled to one another. An analysis based on random decomposition shows that the perturbing defects lie well beyond the first coordination sphere of the probe CO2 molecule and probably cooperate in influencing subsequent reactions. These results suggest caution in interpreting solid state product distributions, even at very low decomposition levels.