High resolution FTIR spectra of CDF3 in the CD stretching fundamental and overtone regions

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Abstract
FTIR spectra of 1 2CDF3 are reported at resolutions up to 0.006 cm− 1 for the CD stretching fundamental and overtone transitions. For the band associated most closely with the CD stretching fundamental, the rotational J and K structure is largely resolved and analysis gives ν̃eff 1=2261.2637 cm− 1, A’=B’=0.329 5858 cm− 1, C’=0.189 0758 cm− 1, D ’ J =3.006×10− 7 cm− 1, D J K =−3.62×10− 7 cm− 1, and D ’ K =1.94×10− 7 cm− 1. (For further constants see Tables I and 2). The large value of B‘−B’=0.001 347 cm− 1 is interpreted in terms of a strong Fermi resonance between ν1 and 2ν2 (symmetrical CF3 stretching vibration) with an effective two‐state coupling constant ‖k 1 2 2‖≂80 cm− 1. Alternatives to this assignment are discussed and it is shown that the two‐state coupling model is only part of a larger coupling scheme involving several states in addition to 2ν2. The rotational structure of the second Fermi resonance component shows severe perturbations for values of K>33. Analysis of 157 assigned lines gives a band center at 2152.2796 cm− 1, with unusual ΔB and ΔC values providing further evidence for multistate interactions. This interpretation is also supported by the structure of the CD overtone transition (2νeff 1=4383.858 cm− 1) and further evidence. The results are discussed in relation to Fermi resonances observed in CHF3 and substantial differences in vibrational redistribution involving the CH and the CD chromophores are observed.