PICOSECOND PHOTOFRAGMENT SPECTROSCOPY .4. DYNAMICS OF CONSECUTIVE BOND BREAKAGE IN THE REACTION C2F4I2-]C2F4+ 2I

Picosecond photofragment spectroscopy of the ultraviolet (UV) photodissociation of 1,2-diiodotetrafluoroethane reveals consecutive breaking of the two C-I bonds. Spin-orbit excited (I*) atoms show a prompt rise, in agreement with a direct mode dissociation of the first bond. Ground-state (I) atoms show a biexponential buildup, one component being fast (≤ 1 ps) while the other component is slow (30-150 ps depending on total energy), characteristic of the second bond breaking. The transient behavior of I atoms changes with the available energy. These results are interpreted in terms of a two step model involving a weakly bound radical. Simulations of transient behavior of I atoms, based on estimated internal energy distributions from the primary step and a model for dissociation rates as a function of energy, suggest that surface crossings are relevant to the dynamics and that the quantum yield of I atoms varies with excitation energy. © 1990 American Institute of Physics.