Determination of absolute photoionization cross sections of the phenyl radical.

Photoionization cross sections of the phenyl radical to form the phenyl cation were measured using tunable vacuum ultraviolet synchrotron radiation coupled with photofragment translational spectroscopy. The phenyl radical was produced via 193- or 248-nm dissociation of chlorobenzene. At 10.0 eV, the photoionization cross sections for the phenyl radical averaged over product channels were found to be 13.4 +/- 2.0 and 13.2 +/- 2.0 Mb, respectively, with very little effect seen from the range of internal excitation produced at the two photolysis wavelengths. Using the photoionization cross section values for each channel, photoionization efficiency curves for the phenyl radical were placed on an absolute scale from 7.8 to 10.8 eV.