Picosecond photofragment spectroscopy. IV. Dynamics of consecutive bond breakage in the reaction C_2F_4I_2→C_2F_4+ 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.
Additional Information© 1990 American Institute of Physics. Received 12 May 1989 Accepted 25 September 1989. This research was supported by the National Science Foundation. We wish to thank Dr. J. L. Knee, Dr. B. Reid, Professor R. Bersohn, and Professor Y. T. Lee for many stimulating discussions. We also thank A. J. Hoffman for help with the experiments and N. Kurur and Dr. J. Yesinowski ( C. I. T. ) for their assistance in obtaining the ^(19)F NMR spectrum of our sample. Finally, we would like to express our sincere thanks to the referee for a critical reading of the manuscript and many helpful comments.
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