engleski

EPR study of solid ethanol

Amorphous solids in comparison with crystals exhibit anomalous dynamics at low temperatures. However, the microscopic nature of processes governing molecular dynamics at temperatures well below the glass transition is still in the focus of the research interest [1]. In this context the application of pulsed electron paramagnetic resonance (EPR) spectroscopy offers the advantage of studying local properties in the vicinity of paramagnetic center. Since solid ethanol can be prepared in phases characterized by different types of disorder [2], it has been used as a very convenient model system for studying low-molecular weight solids by EPR upon incorporation of paramagnetic nitroxyl radicals [3]. In this study ethanol host was doped with TEMPO while electron spin-lattice and phase-memory relaxation times, measured in the temperature interval between 5 and 80 K, were compared for crystalline and glassy states of solid ethanol. In order to delineate the impact of matrix protons on electron spin relaxation the comparison was made between the data acquired with protonated and deuterated host. The largest difference between spin-lattice relaxation rates was detected at lowest temperatures studied and discussed in terms of two level system/boson peak excitations [4]. REFERENCES: 1. Naumov A. V., Vainer Yu. G., and Kador L., Phys. Rev. Lett., 98, 145501 (2007) 2. Ramos. M. A., Rodríguez-Mora V., and Jiménez-Riobóo R. J., J. Phys.: Condens. Matter, 19, 205135 (2007) 3. Kveder M., Merunka D., Jokić M., Makarević J., and Rakvin B., Phys. Rev. B, 80, 052201 (2009) 4. Kveder M., Merunka D., Jokić M., and Rakvin B., J. Chem. Phys., 134, 044531 (2011)

EPR of glassy state; spin relaxation

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