Electron Spin Resonance of an Irradiated Single Crystal of Urea Oxalate

Abstract

Free radicals produced in a single crystal of urea oxalate by gamma‐irradiation have been investigated with the method of electron spin resonance. Only one species of free radical was observed at room temperature. Analysis of the resonance leads to the conclusion that the free radical has the form RCHOH and is probably [Complex chemical formula] with the electron spin density concentrated mostly on the CH carbon. The radical was found to be very stable: Its ESR pattern was observed, essentially undiminished, for more than a year after the irradiation. The g factor was found to be only slightly anisotropic, with principal values: g_u=2.0024, g_v=2.0048, and g_w=2.0047. Couplings with two H nuclei are believed to be those indicated by H⁽¹⁾ and H⁽²⁾, with principal elements of coupling, in gauss, of 15.7, 26.5, and 8.1 for H⁽¹⁾, and of 6.2, —0.3, and 8.3 for H⁽²⁾. With irradiation and observation at 77°K, a different free radical was observed, one with hyperfine structure from only one H, similar to H⁽²⁾.