Abstract
ORGANIC free radicals can be produced by irradiation with ultra-violet light of molecules held in a transparent rigid medium at low temperatures1,2. The method consists in dissolving a suitable substance, D, in a solvent which forms a transparent glass on freezing. The solution is cooled to the temperature of liquid nitrogen and exposed to ultra-violet light. After a time it becomes coloured, and optical absorption spectroscopy shows that free radicals have been created. These radicals persist until the glass is warmed so as to lose its rigidity. Such radicals may be formed in several ways, but the simplest of these is ‘photo-oxidation’1—the ejection of an electron from the illuminated molecule, D. We restrict ourselves to those substances which form radicals only by this process. It seems that the high viscosity of the glassy solvent prevents the recombination of the resulting radical ion, D +, and the ejected electron1.
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