An electron spin resonance study of a γ-irradiated single crystal of glycollic acid

Abstract

Measurements have been made of the electron spin resonance spectrum of a γ-irradiated single crystal of glycollic acid as a function of crystal orientation. These confirm that the trapped radicals are carboxy hydroxy methyl radicals, HOCHCOOH. The results are expressed in the form of a spin Hamiltonian which includes a coupling tensor for the hydrogen attached to the central carbon atom and a tensor for the hydroxyl hydrogen. A special feature of the spectra is that the relative intensities of the hyperfine lines are non-integral, and this is explained by a derivation of the transition moments which shows that the usual selection rule ΔM_I = 0 is inapplicable to the solid state. The anisotropic g tensor is also evaluated. The tensors are briefly discussed in relation to the orientation of the radicals in the crystal and their electronic structure.