Photolysis of Low-Temperature Glasses. II. Temperature and Oxygen Effects in Ethanol and Ether

The effect of temperature and oxygen on the processes occurring in the aromatic solute-sensitized photodecomposition of ethanol and ether glasses is described. The results are discussed in terms of the proposed sensitization mechanism, and they are shown to be in excellent agreement with predictions. The effect of oxygen diffusion (at ∼100°K) is to remove the aromatic solute triplet-state population, the latter being an intermediate in the sensitization mechanism, and thus decrease the rate of radical formation. Oxygen also reacts with any radicals present to form peroxy radicals which are stable to light with wavelengths greater than ∼2500 Å. In the absence of oxygen, the triplet-state population and rate of total radical production are virtually independent of temperature over the range 77° to 125°K. However, the composition of the radical concentration exhibits a strong temperature dependence. It is shown that the latter observation results from a competition between secondary photoreactions (temperature independent) involving the radicals produced by the sensitization process and abstraction reactions (temperature dependent) involving the products of the secondary photoreactions.