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Calculation of the rotational constants A and C for isotopic species of slightly perturbed CH3CN symmetric top molecules

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A technique which was employed earlier to calculate the rotational constants of CH3CCH has been extended to the ground and two vibrational levels in thev 8 vibration of CH3CN for several isotopic species. The moments of inertia and a computer iteration technique over experimental data for each isotopic species were employed to evaluate the constantA v in an excited vibrational state for a symmetric top molecule. This method gave good estimates forA v for each isotope. The angle of bending and the orientation of each molecular system in reference frames, one fixed on the carbon atom at the -C≡N site and the other at the center of mass, were explored. These results are discussed in this paper. The method, which was applied by Tam and Roberts to the nv10,n=1, 2, 3, 4, vibrations of CH3CCH earlier and which was extended to thev 10=1 vibration of CH3CCH with13C isotopic species, has been applied to13C isotopic species of CH3CN and seems to be a useful tool to extract the value ofA 0. Each of these molecules shows reasonable dependency ofA v over vibrational levels. Values ofA v calculated from the geometrical model are in good agreement with those obtained by fitting the terms in the frequency equations, which containedA v , to the experimental data through an iteration technique in which the value ofA was allowed to vary.

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Correspondence to J. A. Roberts.

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Al-Share, M., Hajsaleh, J., Qian, S.W. et al. Calculation of the rotational constants A and C for isotopic species of slightly perturbed CH3CN symmetric top molecules. Struct Chem 5, 109–115 (1994). https://doi.org/10.1007/BF02265352

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Key words

  • Acetonitrile
  • methyl cyanide
  • rovibrational spectra
  • rotational constants
  • microwave spectra
  • v 8 vibration