ELECTRON-SPIN RELAXATION AND ESEEM SPECTROSCOPY OF THE GLYCINE RADICAL IN DIGLYCINE NITRATE SINGLE-CRYSTAL

Glycine radical NH3+-CH-COO- produced by X-ray irradiation was identif ied and characterized by cw-EPR and pulsed EPR methods. The isotropic hyperfine coupling are: H-alpha=2.18 mT, H(NH3)=1.71 mT and N-14=0.3 m T at 295 K. The spin lattice relaxation time was measured in the range 10-200 K by the saturation recovery method, and is described as the s um of the contributions from the: direct process, distribution of the inter-radical couplings and the Murphy process with vibrational energy of 321 cm(-1). The phase memory time T-M was strongly temperature-dep endent with two minima at 20 and 170 K related to the flipping motion of the glycine molecules and rotation of the WH, groups, respectively. The Fourier transform ESEEM spectrum consists of the proton matrix li nes and very sharp lines in the nitrogen frequency region. They are in terpreted as quadrupole frequencies under 'cancellation conditions' wi th quadrupole coupling constant 2.10 MHz. an asymmetry parameter of 0. 7, and N-14 isotropic coupling a(iso)=2.12 MHz of the NH3-group of the neighbouring glycine molecule.