Photodissociation of nitrosobenzene and decomposition of phenyl radical

Photodissociation of nitrosobenzene in a molecular beam has been studied by multimass ion imaging techniques. Photodissociation at 248 nm shows that there is only one dissociation channel, i.e., C₆H₅NO → C₆H₅ + NO, regardless of the fact that the other channel, C₆H₅NO → C₆H₄ + HNO, is energetically accessible in agreement with theoretically predicted results. Photodissociation at 193 nm also shows the same dissociation channel. However, about 10% of the C₆H₅ radicals produced at this wavelength further decomposed into benzyne and H atom, and the dissociation rates of phenyl radical as a function of internal energies were measured. The averaged photofragment translational energies released from the dissociation of nitrosobenzene at 193 and 248 nm are 10.2 and 6.9 kcal/mol, respectively, and fragment distributions are almost isotropic at both wavelengths. In addition, the thermal rate constant for dissociation of C₆H₅NO has been computed and compared with experimental data; the agreement between theory and experiment is excellent, confirming the most recently reported unusually high A-factor (>10¹⁷ s^-1).