The photodissociation dynamics of dibromobenzenes and tribromobenzene in the gas phase studied with femtosecond pump–probe spectroscopy

The photodissociation dynamics of o-, m-, p-dibromobenzene and 1,3,5-tribromobenzene have been investigated in a molecular beam following excitation at 266 nm using ultrafast spectroscopy. In o- and m-dibromobenzene two dissociation pathways have been observed, whereas p-dibromobenzene and 1,3,5-tribromobenzene dissociates via one channel. The channel common for all the compounds has been assigned to predissociation from 1(π,π*) state to the repulsive 3(n,σ*) state. The rate of this process increases with the number of bromine atoms and with decreasing distance on the phenyl ring. The presence of two dissociation channels in o- and m-dibromobenzene is probably related to the lower symmetry of these molecules.