Microwave Spectrum of Benzoyl Fluoride

The rotational transitions of benzoyl fluoride in the ground and first seven excited torsional states, two ``other'' vibrational modes, and the second excited state of one of these ``other'' modes have been assigned. The term values of these states with respect to the ground state have been derived from relative intensity measurements. The term value of the torsional fundamental has been determined to be $\text{59.5 ± 3\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ which gives a twofold barrier to internal rotation of $\text{1560 ± 160\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ for the –COF group. The variation of inertia defect with vibrational state has been used to aid the assignment of in plane or out of plane for the two ``other'' modes. The fundamentals at $\text{168 ± 10\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ and $\text{215 ± 10\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ are tentatively assigned to the out‐of‐plane wag and in‐plane bend, respectively, of the –COF group. There is a close agreement between the observed inertial coefficients in excited torsional states and those derived on the basis of a molecular model with one degree of internal freedom.