INFRARED INTENSITIES IN ClCN, BrCN, AND $CH_{3}CN^{*}$
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Date
1955
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Ohio State University
Abstract
The absolute infrared intensities of the bending and stretching vibrations of ClCN and BrCN, and the bending vibrations of $CH_{3}CN$ have been measured using the Wilson-Wells extrapolation method. From the bending modes and molecular dipole moments, infrared bond moments have been calculated. In Debye units, one obtains for $\mu_{c=n}$ the values $\pm 1.4, \pm 1.3$, and $\pm 1.3$ or $\pm 1.8$ in ClCN, BrCN, and $CH_{3}CN$, respectively; for $\mu_{x-c}$, the values $\pm 1.4, \pm 1.6$, and $\pm$2.6 or $\pm$2.2, where X refers successively to Cl, Br, and $CH_{3}$. Measurements on the skeletal deformation mode of deuterated $CH_{3}CN$ support the choice of the latter pair of moments for this molecule. The relation between the infrared moments and probable static bond moments will be discussed. From the parallel vibrations of the halides, bond moment derivatives have been calculated, and the effect of Fermi resonance between the low frequency stretching fundamental and the first overtone of the bending mode have been estimated by means of a perturbation calculation. Results are compared with the previous work of Nixon and $Cross^{1}$ on ClCN and with other work on related compounds.
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Author Institution: Metcalf Chemical Laboratories, Brown University