The photodissociation dynamics of o-, m- and p-bromotoluene in the gas phase studied with femtosecond pump-probe spectroscopy

The photodissociation dynamics of o-, m- and p-bromotoluene in the gas phase following excitation at 270 nm have been investigated employing femtosecond pump-probe spectroscopy. The initially excited S-1 (pi, pi*) state is predissociative via either the repulsive (3)(n, sigma*) state or via high vibrational levels of the S-0 state. The lifetimes of the S-1 states in the bromotoluene isomers are found to be shorter than in bromobenzene, which is attributed to an increased density of coupled states introduced by the internal rotation of the methyl group. In o-bromotoluene the dissociation process is faster than in the other two isomers, which we ascribe to a higher number of rotational levels available for coupling. (C) 2003 Elsevier B.V. All rights reserved.