The electron spin resonance spectrum of a γ-irradiated single crystal of glycine

It is shown that γ rays act on glycine to give the free radical NH3 +-ĊH-CO2 − which remains trapped in the solid. Electron spin resonance spectra from an irradiated single glycine crystal show marked anisotropy and it is deduced that the radicals are precisely oriented in the crystal lattice. The symmetry shown by the spectra is consistent with that of the crystal lattice. Despite overlapping of lines, the spectra due to the NH3 +-ĊH-CO2 − radical have been interpreted in terms of electronnucleus coupling tensors for the N, the H(C) and the three H(N) nuclei, the latter being equivalent by virtue of a rotation or tunnelling of the -NH3 + grouping. A qualitative interpretation of these tensors in terms of the electronic structure of the radical is given. This is consistent with the negative spin density on the H(C) atoms and a positive spin density on the H(N) atoms, as predicted by theoretical treatments. The radicals appear to be oriented in the lattice in approximately the same way as their parent molecules.