Low temperature electron-spin relaxation in the crystalline and glassy states of solid ethanol

TL;DR

This study investigates electron-spin relaxation in solid ethanol's glassy and crystalline states at low temperatures using EPR spectroscopy, revealing differences in spectral properties, phase memory times, and relaxation mechanisms.

Contribution

It provides new insights into low-temperature spin dynamics and relaxation processes in ethanol's different solid states, highlighting the role of molecular packing and boson peak excitations.

Findings

Shorter phase memory time in crystalline ethanol due to spectral diffusion.

Temperature dependence of relaxation times indicates low-frequency dynamics.

Enhanced energy exchange in ethanol glass linked to boson peak excitations.

Abstract

X-band electron paramagnetic resonance (EPR) spectroscopy was used to study the spectral properties of a nitroxide spin probe in ethanol glass and crystalline ethanol, at 5 - 11.5 K. The different anisotropy of molecular packing in the two host matrices was evidenced by different rigid limit values for maximal hyperfine splitting in the signal of the spin probe. The significantly shorter phase memory time, , for the spin probe dissolved in crystalline ethanol, as compared to ethanol glass, was discussed in terms of contribution from spectral diffusion. The effect of low-frequency dynamics was manifested in the temperature dependence of and in the difference between the data measured at different spectral positions. This phenomenon was addressed within the framework of the slow-motional isotropic diffusion model [S. Lee, and S. Z. Tang, Phys. Rev. B 31, 1308 (1985)] predicting the spin probe dynamics within the millisecond range, at very low temperatures. The shorter spin-lattice relaxation time of the spin probe in ethanol glass was interpreted in terms of enhanced energy exchange between the spin system and the lattice in the glass matrix due to boson peak excitations.