Infrared Absorption of Gaseous Benzoyl Radical C6H5CO Recorded with a Step-Scan Fourier-Transform Spectrometer

A step-scan Fourier-transform infrared spectrometer coupled with a multipass absorption cell was utilized to monitor the gaseous transient species benzoyl radical, C6H5CO. C6H5CO was produced either from photolysis of acetophenone, C6H5C(O)CH3, at 248 nm or in reactions of phenyl radical (C6H5) with CO; C6H5 was produced on photolysis of C6H5Br 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 (nu(6)), the C-C stretching mixed with C-H deformation (nu(15)), the out-of-phase C1C2C3/C5C6C1 symmetric stretching (nu(10)), and the in-phase C1C2C3/C4C5C6 antisymmetric stretching (nu(7)) modes of C6H5CO, respectively. These observed vibrational wavenumbers and relative IR intensities agree with those reported for C6H5CO isolated in solid Ar and with values predicted for C6H5CO 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, C6H5C(O)Br, and C6H5C(O)C6H5 were identified in the C6H5Br/CO/N-2 experiments; the kinetics involving C6H5CO and C6H5C(O)Br are discussed.