Femtosecond photodissociation of triiodide in solution: Excitation energy dependence and transition state dynamics Original Research Article

Femtosecond transient absorption measurements are reported for the photodissociation of triiodide in ethanol solution using 266 nm excitation light. The quantum yield for diiodide formation at this pump wavelength has found to be 0.8, significantly lower than for excitation with 400 nm. Furthermore, the data reveal distinct ultrafast dynamics on a time scale below 300 fs which are associated with the initial evolution of the wavepacket along the symmetric stretching coordinate. Real-time observation of the wavepacket motion at these very early stages of the reaction is made possible through wavelength selective probing, thereby defining detection windows along the nominal reaction coordinate. The results obtained with 266 nm excitation are supplemented by resonant impulsive stimulated scattering experiments. Detailed comparisons with quantum dynamics simulations are intended to provide insight into the time scale of product formation and the nature of the potential energy surface that facilitate the optical probing process.