Vibrational spectra and normal coordinate analysis of CF3OF and CF3OCl

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AbstractThe IR spectra (1400 cm−1 to 160 cm−1) of the gases at ambient temperature and the Raman spectra (below 1400 cm−1) of the liquids near −196°C are reported for CF3OF and CF3OCl. All fundamentals are assigned under Cs symmetry and the results of a normal coordinate analysis are presented. The assignments of Smardzewski and Fox are adopted with one exception for both CF3OF and CF3OCl: the CF3 rock of A″ symmetry is assigned near 430 cm−1 and the two bands between 200 cm−1 and 300 cm−1 are assigned to an A′ fundamental, involving CF3 rocking and COX bending and a Δν=2 transition in the CF3 torsion. An extra band at 548 cm−1 in the Raman spectrum of liquid CF3 COl near −196°C is assigned to a CF3OCl ⃛Cl2 complex. The values of the force constants d(OX) for CF3OX molecules are suggested to be near those for X2O molecules. More than half the normal modes of A′ symmetry show extensive mixing of symmetry coordinates. In some of these cases the symmetry coordinate for which the normal mode is named is the largest but not the dominant contributor to the potential energy distribution, while in others this symmetry coordinate is not even the largest contributor to the potential energy distribution. No normal modes of A′ symmetry are present in which ν(CO), δs(CF3), δ(COX), or δ(CF3) symmetry coordinates are dominant, and the mode conventionally labeled as v(CO) should be labeled as νs(CF3). For the remaining A′ normal modes and all the A″ normal modes, the symmetry coordinate for which the normal mode is named is dominant in the potential energy distribution.