A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C 6H 5CO. C 6H 5CO was produced either from photolysis of acetophenone, C 6H 5C(O)CH 3, at 248 nm or in reactions of phenyl radical (C 6H 5) with CO; C 6H 5 was produced on photolysis of C 6H 5Br at 248 nm. One intense band at 1838 ± 1 cm -1, one weak band at 1131 ± 3 cm -1, and two extremely weak bands at 1438 ± 5 and 1590 ± 10 cm -1 are assigned to the C=O stretching (ν 6), the C-C stretching mixed with C-H deformation (ν 15), the out-of-phase C 1C 2C 3/C 5C 6C 1 symmetric stretching (ν 10), and the in-phase C 1C 2C 3/C 4C 5C 6 antisymmetric stretching (ν 7) modes of C 6H 5CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C 6H 5CO isolated in solid Ar and with values predicted for C 6H 5CO with the B3LYP/aug-cc-pVDZ method. The rotational contours of the two bands near 1838 and 1131 cm -1 simulated according to rotational parameters predicted with the B3LYP/aug-cc-pVDZ method fit satisfactorily with the experimental results. Additional products BrCO, C 6H 5C(O)Br, and C 6H 5C(O)C 6H 5 were identified in the C 6H 5Br/CO/N 2 experiments; the kinetics involving C 6H 5CO and C 6H 5C(O)Br are discussed.