PHOTODISSOCIATION OF CF3I AT 304 NM - EFFECTS OF PHOTON ENERGY AND CURVE CROSSING ON THE INTERNAL EXCITATION OF CF3

We present correlated measurements of the CF3 internal energy, the initial electronic excitation, and the final iodine state in the photodissociation of CF3I at 304 nm by using state-selective photofragment translational spectroscopy. The simultaneous determination of the three properties is achieved by measuring the translational energy distribution of the state-selected iodine fragment as a function of its recoil angle with respect to the electric vector of the photolysis laser. We found that the excited state I*(2p1/2) atoms are formed predominantly from the parallel 3Q0 <-- N transition while the I(2P3/2) atoms are formed from both the perpendicular 3Q1 <-- N transition (70%) and the parallel 3Q0 <-- N transition (30%) followed by curve crossing to the 1Q1 state. By comparing the average internal energies of CF3 produced in the two dissociation channels of the 3Q0 <-- N excitation at 304 nm with the recent results of Felder at 248 nm, we examine the effect of the photon energy and that of the curve crossing on the dynamics of the vibrational excitation. For the I* channel, we observe a strong photon energy dependence of the CF3 internal excitation, suggesting a strong final state interaction in the dynamics of the 3Q0 potential as suggested by a number of model calculations. The best agreement obtained with the model calculation of van Veen et al. supports the assumption of the dominant involvement of the nu2 umbrella vibration. For the 3Q0 component of the I channel, we observe a similar strong photon energy dependence in terms of its slopes, but with an enhanced CF3 internal excitation. This suggests the importance of the curve crossing dynamics as well as the dynamics of the 1Q1 potential. The gross disagreement obtained with the one-dimensional model calculation of van Veen et al. is attributed to the multidimensional nature of the curve crossing process.