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Titolo:
Slow beta process in simple organic glass formers studied by one and two-dimensional H-2 nuclear magnetic resonance. II. Discussion of motional models
Autore:
Vogel, M; Rossler, E;
Indirizzi:
Univ Bayreuth, Inst Phys, D-95440 Bayreuth, Germany Univ Bayreuth Bayreuth Germany D-95440 t Phys, D-95440 Bayreuth, Germany
Titolo Testata:
JOURNAL OF CHEMICAL PHYSICS
fascicolo: 23, volume: 115, anno: 2001,
pagine: 10883 - 10891
SICI:
0021-9606(200112)115:23<10883:SBPISO>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
SECONDARY RELAXATION; SUPERCOOLED LIQUIDS; MOLECULAR-DYNAMICS; VISCOUS LIQUIDS; NMR; TRANSITION; TOLUENE; REORIENTATIONS; GEOMETRY; CHLORIDE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
35
Recensione:
Indirizzi per estratti:
Indirizzo: Vogel, M Univ Bayreuth, Inst Phys, POB 101251, D-95440 Bayreuth, Germany Univ Bayreuth POB 101251 Bayreuth Germany D-95440 reuth, Germany
Citazione:
M. Vogel e E. Rossler, "Slow beta process in simple organic glass formers studied by one and two-dimensional H-2 nuclear magnetic resonance. II. Discussion of motional models", J CHEM PHYS, 115(23), 2001, pp. 10883-10891

Abstract

Applying random walk simulations we analyze results of one- (1D) and two-dimensional (2D) H-2 nuclear magnetic resonance (NMR) experiments carried out to study the slow beta process of toluene-d(5) below the glass transitiontemperature T-g. In this way, we reveal amplitude and mechanism of rotational jumps involved in the secondary relaxation of a rigid molecule. It is shown that essentially all toluene molecules take part in the beta -process. In the glass, nearly independent of temperature, the attributed reorientation is restricted to small solid angles of typically 4 degrees -5 degrees for the majority of particles. Only 10%-20% of the molecules exhibit amplitudes chi > 10 degrees. Concerning the mechanism of this highly restricted motion we demonstrate that the reorientation takes place step-by-step via several elementary rotational jumps one after the other. Assuming thermally activated jumps within energy landscapes which are, first, attributed to a small section of the unit sphere for each respective molecule and, second, chosen in accordance with the distribution of energy barriers g(E-beta) foundin dielectric spectroscopy we succeed in reproducing the results of 1D and2D H-2 NMR experiments on toluene below T-g. (C) 2001 American Institute of Physics.

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Documento generato il 21/09/20 alle ore 06:31:54