  The electron spin-lattice relaxation of TEMPO and TEMPONE was measured at
temperatures between 5 and 80 K in crystalline and glassy ethanol using X-band
electron paramagnetic resonance spectroscopy. The experimental data at the
lowest temperatures studied were explained in terms of electron-nuclear dipolar
interaction between the paramagnetic center and the localized excitations,
whereas at higher temperatures low-frequency vibrational modes from the host
matrix and Raman processes should be considered. The strong impact of hydrogen
bonding between the dopant molecule and ethanol host on the spin relaxation was
observed in ethanol glass whereas in crystalline ethanol both paramagnetic
guest molecules behaved similarly.
