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The ultraviolet photodissociation of 1-bromo-3-fluorobenzene and 1-bromo-4-fluorobenzene at 266 nm has been performed on a universal crossed molecular beams machine combined with the photofragment translational spectroscopy (PTS) detection technique. The time-of-flight (TOF) spectra of Br and FC6H4 photofragments have been measured. The observed translational energy distributions P(E-t) of photofragments revealed that about 46.8 +/- 3.3% and 41.7 +/- 3.0% of the available energy are partitioned into translational energy and the anisotropy parameter beta is 0.7 +/- 0.1 and -0.4 +/- 0.1 for 1-bromo-3-fluorobenzene and 1-bromo-4-fluorobenzene, in accord with that of bromobenzene (-0.7), indicating significant change caused by the fluorine atom substitution. To better interpret the experimental results, ab initio calculations have been performed and the calculation results are in good agreement with the experimental results. A plausible photodissociation mechanism is suggested, and the substitution effect of the fluorine atom is discussed.

The ultraviolet photodissociation of nitrosobenzene at 266 nm has been performed on a universal crossed molecular beams machine with a TOFMS detector. The time-of-flight spectra of the NO and C6H5 photofragments have been measured. The TOF spectra evidence only one component. The measured photofragment translational energy distribution P(E-t) reveals that about 29% of the available energy is partitioned into translational energy. The anisotropy parameter beta at this wavelength is -0.64. From P(E-t) and beta, we deduce that during the photodissociation of C6H5NO, a perpendicular transition dominates over a parallel transition. Ab initio calculations were also performed to interpret the mechanism of the photodissociation.