title: Fast motion in molecular solids at low temperatures: evidence from a pulsed electron paramagnetic resonance study of nitroxyl radical relaxation.
abstract: We have investigated the electron phase-memory relaxation time of the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl at temperatures between 5 and 80 K in crystalline and glassy states of ethanol using pulsed X-band electron paramagnetic resonance spectroscopy. The results indicate that the transition from the slow to fast motion regimes of the paramagnetic center occurs upon further cooling of the sample below ∼20 K. We provide experimental evidence that this phenomenon cannot be ascribed to the impact of hyperfine interactions with methyl protons in the system, but it can be instead a signature of the coupling of the electron spin with the boson peak excitations of the lattice.
authors.affiliation: Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia. kveder@irb.hr
authors.forename: Marina
authors.initials: M
authors.lastname: Kveder
authors.forename: Milan
authors.initials: M
authors.lastname: Jokić
authors.forename: Boris
authors.initials: B
authors.lastname: Rakvin