Infrared Spectra Of CF2=CHD and CF2=CD2: Scaled Quantum-chemical Force Fields And An Equilibrium Structure For 1,1-difluoroethylene

Abstract

Infrared (IR) spectra in the gas phase are reported for CF2=CHD and CF2=CD2 in the region 350-4000 cm(-1). Ab initio calculations of an harmonic force-field and anharmonicity constants have been made with an MP2/aug-cc-pVTZ model. These enable a number of Fermi resonances in each species to be analyzed and a complete set of "observed" harmonic frequencies to be derived. The latter are combined with similar data for CF2=CH2 in a scaling of the model harmonic force field to both anharmonic and harmonic frequencies. Inspection of the scale factors reveals minor defects of the model, evident in the out-of-plane wagging modes and in the CF stretch/CF stretch interaction force constant. Fermi resonance treatments involved in all isotopomers studied are compatible with the overall force-field refinement results. The treatment leaves a small anomaly in the C-13 shift on v(1). Improved microwave spectra are reported for five isotopic species, and a semiexperimental equilibrium structure for F2C=CH2 is determined and compared favorably with the structure obtained from new high-level ab initio calculations. Centrifugal distortion constants are predicted for the five isotopic species, and those for F2C=CH2 are compared with values fit to microwave spectra.

Publisher

American Chemical Society

Publication Date

9-1-2010

Publication Title

Journal of Physical Chemistry A

Department

Chemistry and Biochemistry

Document Type

Article

DOI

https://dx.doi.org/10.1021/jp104498n

Keywords

Correlated molecular calculations, Phase electron-diffraction, Gaussian-basis sets, Vibrational anharmonicity, Microwave spectra, Ab initio calculations, Difluoroethylenes, Butadiene, Hydrogen, Ethylene, Chemistry, physical, Physics, atomic, molecular & chemical

Language

English

Format

text

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