Photodissociation of CF3Br at 193 nm: evidence for a distorted dissociation pathway Original Research Article

The photodissociation of CF3Br at 193 nm has been studied by photofragment translational spectroscopy. The primary dissociation step leads to the formation of CF3 radicals and Br atoms in the electronic ground state and in the spin-orbit excited state, with relative quantum yields φ(Br) = 0.47 ± 0.05 and φ(Br∗) = 0.53 ∓ 0.05, respectively. At higher laser fluences the slowest and internally hottest CF3 radicals undergo photoinduced secondary dissociation to CF2 + F. The anisotropy parameters derived from measurements with a polarized photolysis laser are β(Br) = 1.8 ± 0.2 and β(Br∗) = 0.7 ± 0.3. The experimental results are discussed in terms of a model that involves the initial excitation of two repulsive electronic states 3Q0 and 1Q1 via transitions polarized parallel and perpendicular to the CBr bond, respectively. From the observed β parameters it is concluded that in roughly two thirds of the molecules dissociation proceeds via a distorted geometry in which the molecular symmetry C3v is reduced to Cs through the effect of e-type bending vibrations.