The Infrared Spectrum of the Matrix-Isolated Phenyl Radical

We have measured the infrared absorption spectrum of C(6)H(5), /X (2)A(1), in an Ar matrix at 10 K. The experimental frequencies (cm(-)(1)) and polarizations follow. a(1) modes: 3086, 3072, 3037, 1581, 1441, 1154, 1027, 997, 976, 605; b(1) modes: 972, 874, 706, 657, 416; b(2) modes: 3071, 3060, 1624, 1432, 1321, 1283, 1159, 1063, and 587. Three different methods have been used for the production of the phenyl radicals. Infrared absorption spectra of five deuterated isotopomers, C(6)D(5), p-C(6)H(4)D, p-C(6)HD(4), o-C(6)H(4)D, and m-C(6)H(4)D, were recorded to compare experimental frequency shifts with calculated (UB3LYP/cc-pVDZ) harmonic frequency shifts. The use of CO(2) or NO as internal standards enabled the experimental determination of absolute infrared intensities. The linear dichroism was measured with photooriented samples to establish experimental polarizations of each vibrational band. True gas-phase vibrational frequencies were estimated by considering the gas-to-matrix shifts and matrix inhomogeneous line broadening. The phenyl radical matrix frequencies listed above are within +/-1% of the gas-phase vibrational frequencies. The C(6)H(5) frequencies from this paper supersede our earlier values reported in J. Am. Chem. Soc. 1996, 118, 7400-7401. See also: http://ellison.colorado.edu/phenyl.