ESR Detection of the Cyanogen and Methylene Imino Free Radicals

The electron spin resonance (ESR) spectra of the cyanogen (CN) and methylene imino (H2CN) free radicals trapped in argon have been observed over the temperature range 4.2° to 37°K. The CN radical was produced by the vacuum uv photolysis of HCN in argon. The CN spectrum was a triplet whose outer lines varied with temperature from broad and weak at 4.2°K to narrow and strong at 37°K. This behavior was attributed to the broadening effects of an anisotropic nitrogen hyperfine interaction which was averaged out by the increased motional freedom of the radical at higher temperatures. The isotropic part of the nitrogen hyperfine splitting in CN was estimated to be 4.6 oe. The HCN photolysis also gave some weak ESR lines which were believed to be due to a radical formed by the addition of H atoms to HCN. This was confirmed when this weak spectrum was obtained with much greater intensity by photolyzing HI in the presence of HCN. From an analysis of the ESR spectrum it was shown that the addition of H atoms to HCN gave the H2C=N radical. The two protons each had an isotropic hyperfine splitting of 87.4 oe. The nitrogen hyperfine splitting was anisotropic, the isotropic and anisotropic hyperfine splitting constants being roughly equal and having the numerical value 32 Mc/sec.