Electron Spin Resonance of X-Irradiated Single Crystals of Hydroxyurea

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Abstract
The electron spin resonance of x‐irradiated single crystals of hydroxyurea have been observed and analyzed for different orientations of the crystal in the magnetic field. The free radical responsible for the resonance has been identified as NH2CONH, and the measurements indicate that 41% of the unpaired electron is localized in the 2p orbital of the nitrogen atom. Principal values for the hyperfine coupling constants in gauss are −21.2, −13.5, and −1.5 for H, and 22.5, 1.5, and 1.2 for N. On the basis of these measurements the induced isotropic hyperfine constants for an electron entirely localized in a 2p orbital of the nitrogen atom in the R–N–H radical would be 20.2 G for nitrogen and −31 G for hydrogen. The principal g values are 2.0027, 2.0062, and 2.0108. The results indicate that the trapped radical retains the approximate orientation of the parent molecule in the lattice and that the radical is planar.