title: Infrared spectra of CF(2)=CHD and CF(2)=CD(2): scaled quantum-chemical force fields and an equilibrium structure for 1,1-difluoroethylene.
abstract: Infrared (IR) spectra in the gas phase are reported for CF(2)=CHD and CF(2)=CD(2) 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 CF(2)=CH(2) 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 (13)C shift on nu(1). Improved microwave spectra are reported for five isotopic species, and a semiexperimental equilibrium structure for F(2)C=CH(2) 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 F(2)C=CH(2) are compared with values fit to microwave spectra.
authors.affiliation: School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, United Kingdom.
authors.forename: Donald C
authors.initials: DC
authors.lastname: McKean
authors.forename: Mark M
authors.initials: MM
authors.lastname: Law
authors.forename: Peter
authors.initials: P
authors.lastname: Groner
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Conrad
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Tubergen
authors.forename: David
authors.initials: D
authors.lastname: Feller
authors.forename: Michael C
authors.initials: MC
authors.lastname: Moore
authors.forename: Norman C
authors.initials: NC
authors.lastname: Craig