Infrared Spectra Of 12CF2=12CH2 and 12CF2=13CH2, Quantum-chemical Calculations Of Anharmonicity, And Analyses Of Resonances

Infrared spectra obtained in gas and liquid argon phases are reported for (CF2)-C-12=(CH2)-C-12 and (CF2)-C-12=(CH2)-C-13. These spectra firmly establish the positions of nu(3)(A(1)) and nu(6)(A(2)) for both isotopomers. Using anharmonicity constants from MP2 calculations, Fermi resonances affecting nu(1)(A(1)), nu(2)(A(1)), nu(3), and nu(8)(B-1) are analyzed. Deperturbed fundamental frequencies from these analyses are used in conjunction with unaffected fundamentals and ab initio anharmonicity data to predict all 12 observed harmonic frequencies. A Darling-Dennison type resonance between 2 nu(6) and nu(11) + nu(12) is diagnosed, the calculation of which from ab initio data requires modification of the existing second-order treatment of such constants, where Fermi resonance type terms are also present. Predictions are made of many overtone and combination band frequencies, aiding assignment of observed spectra. From the isolated CH stretching frequency obtained here of 3125.4 cm(-1), the C-H equilibrium bond length is predicted to be 1.0762(11) angstrom