THE INFLUENCE OF THE MOLECULAR-BEAM TEMPERATURE ON THE PHOTODISSOCIATION OF CF3I AT 308 NM

The 308 nm photodissociation of CF3I has been studied by photofragment translational spectroscopy with a polarized photolysis laser. Two overlapping electronic transitions give access to the repulsive states 3Q1 and 3Q0. The initial excitation of the 3Q1 state produces the fragments CF3+I(P-2(3/2)) With a perpendicular recoil anisotropy. In contrast to the 3Q1 state, the 3Q0 state produces photofragments with a parallel recoil. These are CF3+I* (P-2(1/2)), formed in a direct process, and CF3+I(P-2(3/2)), formed via a non-adiabatic transition from the 3Q0 to the 1Q1 state. The photolysis of warmer CF3I molecules was studied by irradiating the early part of the molecular beam pulse. The importance of the 3Q0<--X transition was found to be enhanced due to the absorption from warm molecules. This effect leads to a strong temperature dependence of the I*/I branching ratio at 308 nm, which was found to increase from 0.27 in the coldest part of the beam pulse to 0.92 in the warmer part.