Photofragment translational spectroscopy of 1-bromo-3-fluorobenzene and 1-bromo-4-fluorobenzene at 266 nm

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.