engleski

Spin-lattice relaxation process of the first stable L-alanine radical at cryogenic temperatures

Spin-lattice relaxation process of the first stable L-alanine radical at cryogenic temperatures B. Rakvin Ruđer Bošković Institute, P.O. Box 180, 10002 Zagreb, Croatia The large thermal stability of paramagnetic centers produced by ionizing irradiation of the L-alanine is one of the basic properties, which was involved in alanine/EPR dosimetry. The first stable L-alanine radical, SAR1, yields dominant contribution to composite EPR spectrum of stable paramagnetic species in irradiated L-alanine. Spectroscopic properties of SAR1 center have been studied over many years and it remains the most highly studied paramagnetic center in the L-alanine lattice. However, the dynamic processes associated with the radical motion and influences of intramolecular and intermolecular dynamics on the stability of these centers are still not fully understood. This is not surprising knowing that the dynamic behaviour of CH3 and NH3+ groups produces complex spin relaxation mechanism accompanied with spectral diffusion process in the crystalline lattice. In the present study the dynamic properties of the SAR1 center has been investigated by deducing relaxation spin-spin, T2 and spin-lattice, T1 relaxation times. One expects that SAR1 center can be used as a probe to detect possible intermolecular dynamics. Indeed, an unusually large increase in the effective spin lattice relaxation with decreasing temperature in the low temperature region (20-5K) indicates presence of low frequency mode which could display glassy character and or orientational disorder. The detailed relaxation mechanism and possible origin of such mode will be discussed.

ESR; Relaxation; L-alanine

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