The 280-nm absorption system of benzoyl fluoride

Benzoyl fluoride exhibits a weak, discrete absorption system in the region 290 – 260 nm. Vibrational structure associated with the C₆H₅COF and C₆D₅COF isotopes has been analyzed in detail. The C₆H₅COF and C₆D₅COF origin bands lie at 35 685 and 35 829 cm^?1, respectively. The intensity in the spectrum is principally associated with two progressions, ν′₁₉, the breathing vibration of the benzene ring and ν′₂₄, a COF in-plane bend, and sequence bands involving the COF torsion motion ν₃₆. The $\text{C}{}_6\text{H}{}_5\text{COF}\text{C}{}_6\text{D}{}_5\text{COF}$ν₁₉, ν₂₄, and ν₃₆ vibrational frequencies are respectively 1005/-, $\text{376}\text{357}\text{,}\text{and}\text{57}\text{55}\text{cm}{}^{\mathrm{?1}}$ in the ground state and $\text{950}\text{919}\text{,}\text{348}\text{331}\text{,}\text{and}\text{89}\text{85}\text{cm}{}^{\mathrm{?1}}$ in the excited state. The barriers to rotation of the COF group are estimated from the torsional frequency data to be 1450 and 3450 cm^?1 in the ground and excited electronic states, respectively.