Photofragmentation dynamics of C2H5I and CF3CH2I at 248 nm

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Abstract
Translational photofragment spectroscopy has been used to study the photodissociation dynamics of C2H5I and CF3CH2I at 248 nm. The measured anisotropies of the photofragments show that the initial absorption is the (parallel polarized) 3 Q 0 ← N transition with a dissociation lifetime of 4 ± 2 × 10-13s in both cases. The time of flight measurements yield the energy disposal for channels leading to I (2 P 3/2) and I* (2 P 1/2) for both molecules. The average energy disposed into translation is 62 per cent (I) and 72 per cent (I*) for C2H5I, and 36 per cent (I) and 39 per cent (I*) for CF3CH2I. The quantum yield for I* production is 0·67 ± 0·03 for C2H5I and 0·82 ± 0·07 for CF3CH2I. The results, combined with those of other workers, are compared to an impulsive description of the dissociation dynamics for a variety of substituted alkyl iodides. Finally a simple Landau-Zener curve crossing model is used to highlight the substantial change in curve crossing probability caused by introduction of fluorine atoms at the β position.