Electron spin resonance study on photoinduced changes of the radicals produced in methyl isocyanate solid irradiated with gamma-rays

Abstract Free radicals in the γ-irradiated solid of methyl isocyanate at −196°C have been studied by electron spin resonance (ESR) at −196∼−100°C. An oriented solid of methyl isocyanate was prepared by solidification of methyl isocyanate around an aluminum rod under cooling. The original radical and trapped electron produced by γ-irradiation were recorded at −196°C in the dark. The original radical produced in the oriented solid gave a resonance pattern consisting of a triplet of triplets and was assigned to ·CH2NCO radical. This was converted completely into a new radical on irradiation with visible light for 90 min. The new resonance pattern consists of a triplet of triplets whose nitrogen and proton splitting constants are 20.0 and 87.4 gauss, respectively. The nitrogen hyperfine splitting was anisotropic and the proton splitting constant agreed with that of methylene imino radical (H2C=N·). The new radical was assigned to methylene imino radical. The resonance pattern of ·CH2-NCO radical was restored when the temperature was raised up to −120°C. The mutual conversion between the two radicals by visible light and heat was concluded to be a decomposition of ·CH2NCO into H2C=N· and CO, and a recombination of these two moieties.