Photodissociation of gas phase I3− using femtosecond photoelectron spectroscopy

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Abstract
The photodissociation dynamics of gas phase I3− following 390 nm excitation are studied using femtosecond photoelectron spectroscopy. Both I− and I2− photofragments are observed; the I2− exhibits coherent oscillations with a period of 550 fs corresponding to ∼0.70 eV of vibrational excitation. The oscillations dephase by 4 ps and rephase at 45 and 90.5 ps on the anharmonic I2− potential. The gas phase frequency of ground state I3− is determined from oscillations in the photoelectron spectrum induced by resonance impulsive stimulated Raman scattering. The dynamics of this reaction are modeled using one- and two-dimensional wave packet simulations from which we attribute the formation of I− to three-body dissociation along the symmetric stretching coordinate of the excited anion potential. The photodissociation dynamics of gas phase I3− differ considerably from those observed previously in solution both in terms of the I2− vibrational distribution and the production of I−.