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The motional collapse of the methyl C-H stretching vibration bands

Publication ,  Journal Article
MacPhail, RA; Snyder, RG; Strauss, HL
Published in: The Journal of Chemical Physics
January 1, 1982

The asymmetric CH stretching bands of the methyl groups of a number of alkane systems have been examined as a function of temperature. At low temperatures, two bands are seen for a CH3 group. These bands collapse into one as the temperature is raised. Examination of crystals of alkanes with both odd and even numbers of carbon atoms, alkanes in urea clathrates, and deuterium substituted alkanes allows the separation of intramolecular and intermolecular contributions to the band splittings and widths. Model Hamiltonians that express the stretching energy levels as a function of both the methyl torsional coordinates and the external coordinates of the alkanes are set up. These are used in the Redfield equations to derive expressions for the splittings and widths in terms of parameters which give the coupling of the various types of motion. The splittings are found to be proportional to the average of cos 5θ, where θ is the torsional angle, and a contribution to the width is found to be due to fluctuations in this quantity. Comparison of the equations with the observed widths shows that the relaxation times of the torsional motion, which are greater than 0.2 but less than about 20 ps, are fast enough to yield the motionally narrowed limit for the spectrum as required in the derivation of the Redfield equations. © 1982 American Institute of Physics.

Duke Scholars

Published In

The Journal of Chemical Physics

DOI

ISSN

0021-9606

Publication Date

January 1, 1982

Volume

77

Issue

3

Start / End Page

1118 / 1137

Related Subject Headings

  • Chemical Physics
  • 51 Physical sciences
  • 40 Engineering
  • 34 Chemical sciences
  • 09 Engineering
  • 03 Chemical Sciences
  • 02 Physical Sciences
 

Citation

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MacPhail, R. A., Snyder, R. G., & Strauss, H. L. (1982). The motional collapse of the methyl C-H stretching vibration bands. The Journal of Chemical Physics, 77(3), 1118–1137. https://doi.org/10.1063/1.443996
MacPhail, R. A., R. G. Snyder, and H. L. Strauss. “The motional collapse of the methyl C-H stretching vibration bands.” The Journal of Chemical Physics 77, no. 3 (January 1, 1982): 1118–37. https://doi.org/10.1063/1.443996.
MacPhail RA, Snyder RG, Strauss HL. The motional collapse of the methyl C-H stretching vibration bands. The Journal of Chemical Physics. 1982 Jan 1;77(3):1118–37.
MacPhail, R. A., et al. “The motional collapse of the methyl C-H stretching vibration bands.” The Journal of Chemical Physics, vol. 77, no. 3, Jan. 1982, pp. 1118–37. Scopus, doi:10.1063/1.443996.
MacPhail RA, Snyder RG, Strauss HL. The motional collapse of the methyl C-H stretching vibration bands. The Journal of Chemical Physics. 1982 Jan 1;77(3):1118–1137.

Published In

The Journal of Chemical Physics

DOI

ISSN

0021-9606

Publication Date

January 1, 1982

Volume

77

Issue

3

Start / End Page

1118 / 1137

Related Subject Headings

  • Chemical Physics
  • 51 Physical sciences
  • 40 Engineering
  • 34 Chemical sciences
  • 09 Engineering
  • 03 Chemical Sciences
  • 02 Physical Sciences