The kinetic and internal energy of NO from the photodissociation of nitrobenzene

Article abstract of DOI:10.1063/1.466547

Laser induced fluorescence probing of the nitric oxide fragment determines the distribution of rotational and vibrational energies of NO produced in the 226 and 280 nm photolysis of nitrobenzene.Combining these results with kinetic energy measurements using vaccum ultraviolet photoionization to detect the fragment gives a detailed view of the energy release in the photolysis.Boltzmann distributions describe the rotational state populations at both photolysis wavelengths.The rotational temperature of NO from the 226 nm photolysis is (3700+/-350) K, corresponding to an average rotational energy of (0.32+/-0.03) eV, and that of NO from the 280 nm photolysis is (2400+/-200) K, corresponding to an average rotational energy of (0.20+/-0.03) eV.We observe no vibrationally excited NO and place an upper limit of 10percent on the fraction of nitric oxide produced in any one vibrationally excited state.Two different limiting models, impulsive energy release and statistical energy redistribution, both corrrectly predict much more rotational than vibrational excitation, but neither completely describes the observed internal and kinetic energies.The impulsive model finds more NO rotational and translational energy, but much less phenoxy fragment internal energy than we observe.The statistical model does better for the NO rotation and phenoxy fragment internal energy, but underestimates the translational energy substantially.A combination of these two types of behavior provides a physical picture that qualitatively explains our observations.It is likely that statistical energy redistribution occurs during the approach to the transition state for isomerization of nitrobenzene to phenyl nitrite and impulsive energy release dominates during the subsequent rupture of the CO-NO bond.