Raman and infrared study of reorientational dynamics in trifluorobenzene

Yuan, Peng; Chen, A. F. T.; Schwartz, M.

doi:10.1002/jrs.1250200106

Cited by 7 publications

(2 citation statements)

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“…In contrast to the other two liquids, there are very few reported time-domain measurements of the reorientational dynamics in liquid 1,3,5-C 6 F 3 H 3 . Raman spectral bandwidth data for the two a‘ vibrations of 1,3,5-C 6 F 3 H 3 yield a reorientation time of 6.7 ps at 296 K . The reorientation time is extracted in the usually way by subtracting the line width of the isotropic Raman band from that of the depolarized Raman band.…”

Section: Resultsmentioning

confidence: 99%

“…36,37 From the OHD-RIKES data, a reorientation time of 9.05 ( 0.10 ps is obtained for liquid 1,3,5-C 6 F 3 H 3 . In contrast to the other Raman spectral bandwidth data for the two a′ vibrations of 1,3,5-C 6 F 3 H 3 yield a reorientation time of 6.7 ps at 296 K. 40 The reorientation time is extracted in the usually way by subtracting the line width of the isotropic Raman band from that of the depolarized Raman band. Although this value of the reorientation time is less than the value obtained in this study, it is not unreasonable, given that reorientation times from Raman line shapes are not as accurate as those obtained directly from the diffusive part of OHD-RIKES response.…”

Section: Resultsmentioning

confidence: 99%

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Structure and Intermolecular Dynamics of Liquids: Femtosecond Optical Kerr Effect Measurements in Nonpolar Fluorinated Benzenes

1997

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A comparative study of the collective polarizability anisotropy dynamics of benzene, 1,3,5-trifluorobenzene, and hexafluorobenzene was carried out by using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES) with 45 fs laser pulses. The OHD-RIKES data were analyzed by using a modeldependent approach and a Fourier transform approach, which yields a spectral density for the liquid. From an analysis of the long-time tails, collective reorientation times of 2.45 ( 0.06, 9.05 ( 0.10, and 13.5 ( 0.1 ps were obtained respectively for C 6 H 6 , 1,3,5-C 6 F 3 H 3 , and C 6 F 6 . The spectral densities are narrower for 1,3,5-C 6 F 3 H 3 and C 6 F 6 than for C 6 H 6 by roughly a factor of 2. Information about the intermolecular vibrational modes of the liquid is contained in the reduced spectral density which is obtained by subtracting the tailmatched diffusive reorientational response from the OHD-RIKES data. In the case of C 6 H 6 and C 6 F 6 , the intermolecular spectral density can be decomposed into at least two broad overlapping bands. In contrast, the intermolecular spectral density for 1,3,5-C 6 F 3 H 3 is characterized by a single band. These spectra are rationalized in terms of the librational dynamics of perpendicular dimers in liquid C 6 H 6 and C 6 F 6 and parallel dimers in liquid 1,3,5-C 6 F 3 H 3 .

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Structure and Intermolecular Dynamics of Liquids: Femtosecond Optical Kerr Effect Measurements in Nonpolar Fluorinated Benzenes

1997

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Rotational diffusion in methyl iodide: Bandshape analysis of degenerate vibrational modes

Wang

Yuan

Schwartz

1989

J Raman Spectroscopy

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The Raman spectral bandshapes of the v,(A ,), v,(A ,) and v4(E) vibrations of CH,I were studied as a function of temperature in the liquid phase. Perpendicular diffusion coefficients calculated from v, agreed well with earlier reported results. The degenerate CH, stretching vibration, v4, was analyzed via fitting by a model incorporating two Lorentzian lineshapes. Values of the parallel diffusion constants, Dll , determined using only the narrower component were in excellent semi-quantitative agreement with those predicted by the free rotor model of molecular reorientation. Analysis of the room-temperature Raman spectrum of vs(@ yielded the same value of Dll as that calculated from v., . The room-temperature infrared spectral intensities of v5 were fitted by a model with a narrow Lorentzian containing contributions from rotational and vibrational relaxation superposed on a second component introduced to account for the broad background absorption. Dll determined from the IR bandwidth was in good agreement with values obtained from the Raman spectra of v, and v5. These results demonstrate the utility of analyzing degenerate vibrational modes to determine the parallel diffusion Coefficients in C,, molecules.Analysis of the isotropic and anisotropic Raman linewidths of totally symmetric vibrations is a well established, reliable technique for the determination of 'tumbling' rotational diffusion coefficients (Dl) of symmetric top molecules in 1 i q~i d s . l~~ More recently, a number of researchers have successfully utilized various methods of estimating vibrational relaxation contributions (A,,) to the bandwidth to extract the 'spinning' diffusion constants ( D 11) from the doubly degenerate vibrations of molecules of D6h4,5 and D,h6-9 symmetry. To date, however, attempts to determine Dll for molecules of C,, or lower symmetry from Raman spectra of the degenerate (E) modes have proved unsuccessful owing to the more complex dependence of the lineshape on D, , Dl, and A, .1--3*10In order to ascertain whether reliable estimates of the parallel diffusion coefficients can be calculated from the degenerate vibrations of C,, molecules, we have measured the Raman bandshapes of the v4(CH, antisymmetric stretch), v,(CH, symmetric stretch) and v,(C-I stretch) modes of methyl iodide as a function of temperature in the liquid phase. The derived values of D II are compared with results from room-temperature Raman and infrared bandshapes of the v5(CH, stretch) vibrational mode and with the predictions of current theories of rotational diffusion. VIBRATIONAL BANDSHAPES OF DEGENERATE MODES IN C,, MOLECULESAssuming a statistically independent, exponentially decaying, vibrational relaxation correlation function [G,(t) = exp( -t/.r,)] and small-step rotational diffusion, the total correlation function for Raman vibrations of E symmetry in C3, molecules is the sum of two exponential terms:2The coefficient A is a function of the spherical components, b',\ and by',, of the polarizability derivative tensor, and the correlation times are gi...

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