Density dependence of rotational relaxation of supercritical CF3H

Okazaki, Susumu; Matsumoto, Masayuki; Okada, Isao; Maeda, Katsutoshi; Kataoka, Yosuke

doi:10.1063/1.470118

Cited by 44 publications

(39 citation statements)

References 40 publications

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“…Recent Raman scattering studies of pure supercritical fluids have shown that the form of the rotational correlation function depends on density. [10,11] In these studies the calculated rotational relaxation times had values of less than 1 picosecond which is comparable to the inverse of the collision frequency at low density. As the density increases the rotational correlation functions of the pure solvents exhibit a transition from free rotor to diffusive behavior.…”

Section: Rotationalmentioning

confidence: 73%

Rotational Diffusion and Trans-cis Isomerization of Substituted Diphenyl Polyenes in the Compressible Region of Supercritical Fluids.

Kauffman

Wiemers

Khajehpour

1998

THE REVIEW OF HIGH PRESSURE SCIENCE AND TECHNOLOGY

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We examine rotational diffusion and trans-cis isomerization of two Biphenyl polyenes, diphenylbutadiene (DPB) and hydroxymethyl-stilbene (HMS) in supercritical fluid CO2 and ethane. The results of density dependent rotational diffusion measurements are interpreted using a model which we have recently developed for rotational diffusion in compressible fluids. Comparison of DPB and HMS fluorescence lifetimes indicate that the rate of the isomerization reaction of DPB is nearly independent of density while HMS exhibits a strong density dependence in CO2. Analysis of the HMS data using Kramers theory indicates that the density dependence is the result of solvent-solute frictional interactions.

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Section: Rotationalmentioning

confidence: 73%

Rotational Diffusion and Trans-cis Isomerization of Substituted Diphenyl Polyenes in the Compressible Region of Supercritical Fluids.

Kauffman

Wiemers

Khajehpour

1998

THE REVIEW OF HIGH PRESSURE SCIENCE AND TECHNOLOGY

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“…In CF 3 H at low reduced densities, we observed an additional shoulder at ∼535 nm ( Figure 1, lower panel). This shoulder corresponds to a shift of ∼3000 cm -1 from the excitation wavelength (458 nm) and we conclude that it is due to Raman scatter from the ν 1 symmetric stretching mode of CF 3 H. 60 The steady-state behavior in supercritical fluids can be summed up as follows. Fluid density has little influence on the emission characteristics of BTBP in either supercritical CF 3 H or CO 2 .…”

Section: Resultsmentioning

confidence: 98%

Probing the Scale of Local Density Augmentation in Supercritical Fluids: A Picosecond Rotational Reorientation Study

Heitz

Bright

1996

J. Phys. Chem.

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We report on the rotational reorientation kinetics of N, 4,9, in several liquids and in three supercritical fluids (fluoroform, carbon dioxide, and ethane). In liquids, BTBP follows near perfect Debye-Stokes-Einstein (DSE) behavior under sticky boundary conditions. However, in supercritical fluids the rotational dynamics of BTBP are distinctly different. In close proximity to the critical density (F r ≈ 1), the recovered rotational reorientation times are up to 12-fold greater than predicted by simple DSE theory with sticky boundary conditions. Upon increasing the fluid density, the recovered rotational reorientation times steadily decrease until they fall within hydrodynamic predictions (i.e., DSE theory). This extraordinary behavior is explained in terms of local solute-fluid density augmentation which is a feature particular only to supercritical fluids. The local density augmentation surrounding the solute is quantified in several ways. By using a model recently developed by Anderton and Kauffman (J. Phys. Chem. 1995, 99, 13759), the local fluid density is found to exceed the bulk by up to 300%. Upon increasing the pressure and moving away from the high compressibility region we see that the extent of local density augmentation decreases to a value approaching the bulk density. In an alternative interpretation, we explain the observed rotational reorientation dynamics in terms of the size of the solutefluid cluster. At low fluid density (near the critical density) the radius of the "solute-fluid cluster" is a factor of 2 greater than the solute alone. Again, as pressure is increased, there is a decrease in the cluster size and the radius of the reorienting species (BTBP + clustered fluid molecules) approaches the predicted value based on DSE theory using friction/boundary terms determined for BTBP in normal liquid solvents.

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“…In addition, it was observed from a Raman spectroscopic study by Okazaki et al that the inversion is evident below half the critical density for supercritical CF 3 H ͑the fact that CF 3 H involves a weaker intermolecular interaction than water is reflected in the higher inversion density͒. 66 Thus, the apparent disagreement is present in the density dependence between the results from the NMR and simulations and those from Okada et al's dielectric relaxation measurements performed in the frequency range up to 40 GHz.…”

Section: Resultsmentioning

confidence: 99%

Structural study of supercritical water. III. Rotational dynamics

Matubayasi

Nakao

Nakahara

2001

The Journal of Chemical Physics

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The rotational dynamics of water in super-and subcritical conditions is investigated by measuring the spin-lattice relaxation time T 1 of heavy water (D 2 O). The experimentally determined T 1 is shown to be governed by the quadrupolar relaxation mechanism even in the supercritical conditions and to provide the second-order reorientational correlation time 2R of the O-D axis of a single water molecule. It is then found that while 2R decreases rapidly with the temperature on the liquid branch of the saturation curve, it remains on the order of several tens of femtoseconds when the density is varied up to twice the critical at a fixed supercritical temperature of 400°C. The comparison of 2R with the angular momentum correlation time shows that the rotational dynamics is not diffusive in supercritical water. The dependence of 2R on the hydrogen bonding state is also examined in combination with molecular dynamics simulations, and the effect of the hydrogen bonding on the rotational dynamics in supercritical water is found to be weaker than but to be on the same order of magnitude as that in ambient water on the relative scale. Actually, although 2R is divergent in the limit of zero density, it is observed to increase with the density when the density is above ϳ1/3 of the critical.

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Density dependence of rotational relaxation of supercritical CF3H

Cited by 44 publications

References 40 publications

Rotational Diffusion and Trans-cis Isomerization of Substituted Diphenyl Polyenes in the Compressible Region of Supercritical Fluids.

Rotational Diffusion and Trans-cis Isomerization of Substituted Diphenyl Polyenes in the Compressible Region of Supercritical Fluids.

Probing the Scale of Local Density Augmentation in Supercritical Fluids: A Picosecond Rotational Reorientation Study

Structural study of supercritical water. III. Rotational dynamics

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