Proton and carbon-13 hyperfine interaction in the electron spin resonance spectrum of krypton-isolated ethynyl radical at low temperatures

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Abstract
The electron spin resonance (ESR) spectrum of the ethynyl radical, ĊCH, isolated in a krypton matrix at 4.2°K, has been measured. The radical was produced by the photolysis of acetylene with radiation from microwave discharge in hydrogen gas. The observation of the hydrogen atom ESR spectrum suggests that the mechanism of the formation of ethynyl radical is the photolytic decomposition, C2H2+hv → C2H+H, and this has been confirmed by the photolysis of C2D2 and 13C2H2. Analysis of the ESR spectra leads to the following g and hyperfine interaction parameters, with the parallel direction being taken along the C–C bond: g∥=2.0026±0.00005, g⊥=2.0017±0.00005; A∥(H)=18.1±0.1 G, A⊥(H)=15.1±0.1 G; A∥(13Cα)=357.2±0.5 G, A⊥(13Cα)=317.3±0.5 G; A∥(13Cβ)=67.7±0.5 G, A⊥(13Cβ)=50.6±0.5 G; a(H)=16.1±0.1 G; a(13Cα)=331.2±0.5 G; and a(13Cβ)=55.9±0.5 G. The above hyperfine interaction data are compared with corresponding theoretical estimates presently available.