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Published April 15, 2003 | Published
Journal Article Open

Femtosecond dynamics of solvated oxygen anions. I. Bifurcated electron transfer dynamics probed by photoelectron spectroscopy

Abstract

The ultrafast dissociationdynamics of O−_6⋅X (X=O_2, N_2, Xe, or N_2O) was investigated by femtosecondphotoelectron spectroscopy. The transients, monitoring nascent O−_2, exhibit biexponential rises with two distinct time constants—the fast component (τ_1∼200 fs) corresponds to the joint rate constant for electron recombination and direct dissociation of the O−_4 core perturbed by solvent molecules, whereas the slow component (τ_2=2.0–7.7 ps, depending on the solvent) corresponds to the process for the liberation of O−_2, which is governed by vibrational predissociation and intramolecular vibrational-energy redistribution. These observations are consistent with the mechanism proposed in the earlier communication of this work [Paik et al., J. Chem. Phys. 115, 612 (2001)]. The wave packet bifurcates via two separate dissociation pathways: electron transfer followed by electron recombination, and electron transfer followed by vibrational predissociation. Unlike all other solvents, the anomalous behavior observed for O−_6⋅N_2O—a threefold increase in τ_2 value, compared to the other solvents, and a factor of 10 increase for τ_2, compared to that of O−_6—reflects the more effective energy dissipation via solute–solvent vibration-to-vibration and rotational couplings. Moreover, for all solvents, the ratio of the slow-rise contribution to the total signal can be correlated with the degree of cooling, supporting the concept of bifurcation in the two channels.

Additional Information

© 2003 American Institute of Physics. Received 10 October 2002; accepted 23 January 2003. Published online 31 March 2003. This work was supported by the National Science Foundation and the AFOSR. We wish to thank Dr. T. M. Bernhardt for helpful discussion in the initial stage of this work (Ref.9).

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