Analysis of the 254.7 nm absorption system of carbonyl fluoride

The 230 nm absorption spectrum of carbonyl fluoride has been recorded in the vapor phase at 25° and −78 °C at path lengths up to 48 m. In all, 170 bands were observed in the spectrum and were assigned to vibrational activity in ν1′, ν2′, ν3′, ν4′, and ν5′. The presence of temperature sensitive bands attributed to ν4′′ leads to the interpretation that the excited state is nonplanar. Combination differences isolating ν4′′ show that the inversion doubling splitting is less than the experimental error for levels 4+ and 4− in the Q4 mode of vibrational excitation. A fit of the G4 term values to the energy levels derived from a quadratic-Lorentzian function yielded a central barrier of 8200 cm−1 and an out-of-plane angle of 31.8° for V(Q4). The high barrier is attributed to an inductive effect from the fluorine atoms brought about by a relaxation of the symmetry from C2v to Cs on electronic excitation.