Evidence of vibrational mode coupling in 2-fluoroethanol via high-resolution infrared spectroscopy in a molecular beam

1994

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The high resolution IR spectrum of cyclobutane in a supersonic molecular beam was obtained for the region of 2981 to 2991 cm-1. The spectrum reveals four overlapping bands suggestive of vibrational mode coupling in the C-H stretching region. Ground -state combination differences demonstrate that these bands__ Ac_:e io For originate from 2 different ground states, the symmetric and INT IS CF-., asymmetric ring puckering states. Evidence of vibrational mode, ' coupling is present in all four bands. The coupling depends on' J both J and the symmetry of the puckering state. A model:. coupling scheme involving two qualitatively different types of y couplings is developed to explain the observed spectrum.. -----------Symmetry restrictions and the Interaction between molecular" rotation and ring puckering qualitatively accounts for the[ dramatically different coupling behavior between the two ring/ puckering states.

Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

High resolution infrared spectroscopy of cyclobutane: A study of vibrational mode coupling involving large amplitude, low frequency modes

Miller

1994

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] Frequently, IVR is viewed as an explicitly resolved data and discuss in detail the application of these mechanisms to mode-coupling in the mid-sized molecule pyrizine. 10 From these as well as other experiments 4 -13 , it is clear that rotational angular momentum can play an important role in state mixing, and our understanding of the physical mechanism of rotation dependent vibrational mode-coupling is far from complete.…”

Section: Intramolecular Vibrational Energy Redistribution (Ivr) Has Bmentioning

confidence: 99%

“…[4][5][6][7][8] Perturbations in the spectra of many molecules lead to the appearance of clusters of peaks where one would expect to see a single ro-vibrational transition. These clusters or clumps of peaks are direct evidence of state coupling.…”

Section: Intramolecular Vibrational Energy Redistribution (Ivr) Has Bmentioning

confidence: 99%

Vibrationally induced rotational axis switching: A novel mechanism for vibrational mode coupling

Ezra

1992

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High resolution IR spectra of small-to medium-sized molecules such as 2-fluoroethanol (2FE) show that the effective density of coupled states is often greater than that obtained by a direct count of vibrational states. A novel mechanism for rotation-vibration interaction, vibrationally induced rotational axis switching (VIRAS), is proposed as a possible explanation for these discrepancies. VIRAS has its origin in centrifugal distortion, and is physically distinct from Coriolis coupling. In the case of 2FE, we explicitly treat the coupling of overall rotation with large-amplitude internal rotation about the C-C bond. Assuming a uniform coupling of all dark vibrationtorsion states to the bright state, we predict a density of coupled states in good agreement with that observed in the C-H stretching region at 2980 cm -1 .

“…Our group has been investigating a homologous series of substituted ethanes which include GgЈ-2-fluoroethanol ͑2FE͒, g-1,2-difluoroethane ͑DFE͒, and t-1-chloro-2-fluoroethane ͑trans CFE͒. [9][10][11][12] The substituted ethanes in this series have varying degrees of van der Waals interaction that hinder internal rotation. In contrast to the molecules studied by Parmenter, these substituted ethanes have a stronger interaction and a lower density of available states.…”

Section: Introductionmentioning

confidence: 99%

Linking structure and vibrational mode coupling using high-resolution infrared spectroscopy: A comparison of gauche and trans 1-chloro-2-fluoroethane

Miller

Stone

1995

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High resolution spectroscopy of 1,2difluoroethane in a molecular beam: A case study of vibrational modecoupling J. Chem. Phys. 97, 2971 (1992; 10.1063/1.463038 Microwave, infrared, and Raman spectra, structures, quadrupole coupling constants, barrier to internal rotation, and vibrational assignment of 1chloro2methylpropene Spectra and structure of chiral molecules. III.a) Vibrational assignment and normal coordinate analysis of 1bromo 1chloro1fluoroethane and 1bromo1chloro1fluoroethane?2d 1The high-resolution infrared spectrum of 1-chloro-2-fluoroethane in a molecular beam was collected over the 2975-2994 cm Ϫ1 spectral region. The spectral region of 2975-2981 cm Ϫ1 contains a symmetric C-H stretching vibrational band of the gauche conformer containing the 35 Cl isotope. The spectral region of 2985-2994 cm Ϫ1 contains three vibrational bands of the trans conformer. Two of the three bands are assigned as an antisymmetric C-H stretch of each of the two different chlorine isotopes. The third band is assigned as a symmetric C-H stretch of the 35 Cl isotope. The gauche conformer of 1-chloro-2-fluoroethane showed doublet patterns similar to those previously observed in 1,2-difluoroethane. The model for 1,2-difluoroethane is further refined in the present work. These refinements suggest that the coupling dark state in 1,2-difluoroethane is composed of 1 quantum C-H bend, 1 quantum C-C stretch, and 12 quanta of torsion. For 1-chloro-2-fluoroethane the dark state could not be identified due to a small data set. The trans conformer of 1-chloro-2-fluoroethane showed no evidence of mode coupling in the three vibrational bands. Including 2-fluoroethanol in this series of molecules, the extent of vibrational mode coupling did not correlate with the density of states available for coupling. Therefore, density of states alone is insufficient to explain the observed trend. A correlation was observed between the degree of intramolecular interaction and vibrational mode coupling.