Infrared Spectra of CF2=CHD and CF2=CD2; Scaled Quantum-Chemical Force Fields and an Equilibrium Structure for 1,1-Difluoroethylene

Donald C. McKean, Mark McGregor Law, Peter Groner, Andrew R. Conrad, Michael J. Tubergen, David Feller, Michael C. Moore, Norman C. Craig

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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 13C shift on ¿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.
Original languageEnglish
Pages (from-to)9309-9318
Number of pages10
JournalJournal of Physical Chemistry A
Volume114
Issue number34
Early online date6 Aug 2010
DOIs
Publication statusPublished - 2 Sep 2010

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