Photodissociation of bromochlorobenzenes

The photodissociation kinetics of 2-, 3- and 4-bromochlorobenzene (BrClPh) and bromo-3,5-dichlorobenzene (Br-diClPh) have been studied in a molecular beam following excitation at 270 nm using femtosecond pump-probe spectroscopy. The kinetics and the dissociation dynamics in the BrClPhs were found to resemble the BrFPhs much more than the BrBrPhs. In 2- and 3-BrClPh two dissociation channels were observed, whereas 4-BrClPh and Br-3,5-diClPh dissociates via only one channel. The time constant for channel one, present in all molecules, depends on the number of chlorine atoms and their position. The absence of a second channel in 4-BrClPh is a general property among mixed Br-(Br, Cl or F)-Phs and is likely to be due to a dissociation channel involving a triplet excitation.