Photodissociation of bromobenzene at 266 nm

The photodissociation of C6H5Br at 266 nm has been investigated on the universal crossed molecular beam machine, and time-of-flight spectra as well as the angular distribution of Br atom have been measured. Photofragment translational energy distribution P(E-t) reveals that about 47% of the available energy is partitioned into translational energy. The anisotropy parameter beta at this wavelength is -0.7+/-0.2. From P(E-t) and beta, we deduce that C6H5Br photodissociation is a fast process and the transition dipole moment is almost perpendicular to the C-Br bond. Ab initio calculations have been performed, and the calculated results show that the geometry of the first excited state of bromobenzene has changed apparently compared with that of the ground state. Two kinds of possible fast dissociation mechanism have also been proposed. (C) 1999 American Institute of Physics. [S0021-9606(99)01206-4].