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Titolo:
Raman free-induction-decay measurements in low viscosity and supercooled toluene: Vibrational dephasing by shear fluctuations
Autore:
Hubble, HW; Lai, TS; Berg, MA;
Indirizzi:
Univ S Carolina, Dept Chem & Biochem, Columbia, SC 29208 USA Univ S Carolina Columbia SC USA 29208 m & Biochem, Columbia, SC 29208 USA
Titolo Testata:
JOURNAL OF CHEMICAL PHYSICS
fascicolo: 8, volume: 114, anno: 2001,
pagine: 3662 - 3673
SICI:
0021-9606(20010222)114:8<3662:RFMILV>2.0.ZU;2-V
Fonte:
ISI
Lingua:
ENG
Soggetto:
VISCOELASTIC CONTINUUM MODEL; FEMTOSECOND SOLVATION DYNAMICS; PHOTON-ECHO EXPERIMENTS; NONPOLAR SOLVATION; MOLECULAR LIQUIDS; RELAXATION PROCESSES; HYDRODYNAMIC THEORY; ATTRACTIVE FORCES; SCATTERING; ACETONITRILE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
58
Recensione:
Indirizzi per estratti:
Indirizzo: Hubble, HW Univ S Carolina, Dept Chem & Biochem, Columbia, SC 29208 USA Univ S Carolina Columbia SC USA 29208 , Columbia, SC 29208 USA
Citazione:
H.W. Hubble et al., "Raman free-induction-decay measurements in low viscosity and supercooled toluene: Vibrational dephasing by shear fluctuations", J CHEM PHYS, 114(8), 2001, pp. 3662-3673

Abstract

Total dephasing decay profiles of the nu (12) (1002 cm(-1)) ring-stretching mode of toluene have been measured in the time domain in a range extending from the low viscosity, normal liquid (380 K, 0.26 cP) to the high viscosity, supercooled liquid (140 K, 4600 cP). In the region from 1 to 5 cP (250to 200 K), the profile makes a transition from exponential to partially Gaussian, consistent with a loss of motional narrowing. In contrast to many interpretations of dephasing in terms of collisional dynamics, these data clearly indicate an important role for diffusive dynamics in vibrational dephasing. Above 10 cP, oscillations appear, and their period decreases with increasing viscosity. An analysis of the low to moderate viscosity region with a Kubo model shows that the frequency modulation time is dependent on theviscosity. The dephasing decay profiles are used to test a recent viscoelastic theory of dephasing [Chem. Phys. 233, 257 (1998)], which attributes the perturbation of the vibrational frequency to shear fluctuations in the liquid. A second dephasing process must be included to obtain reasonable fitsin the viscosity range below 10 cP. The second process is consistent with a Gaussian frequency modulation whose modulation time is weakly viscosity dependent or has no viscosity dependence. We speculate that this process is due to rapid rotation about the toluene z axis and that the same process also causes the oscillations seen at higher viscosity. There is a good correspondence between the value of the infinite frequency shear modulus found from fitting the Raman free-induction-decay data and the value recently foundby Larsen, Ohta, and Fleming by fitting photon-echo-peak-shift measurements in toluene [J. Chem. Phys. 111, 8970 (1999)]. This correspondence supports the idea that both vibrational dephasing and nonpolar electronic solvation are caused by the same physical mechanism. (C) 2001 American Institute ofPhysics.

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Documento generato il 30/11/20 alle ore 01:59:41