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Femtosecond dynamics of solvated oxygen anions. II. Nature of dissociation and caging in finite-sized clusters

Kim, Nam Joon and Paik, D. Hern and Zewail, Ahmed H. (2003) Femtosecond dynamics of solvated oxygen anions. II. Nature of dissociation and caging in finite-sized clusters. Journal of Chemical Physics, 118 (15). Art. No. 6930. ISSN 0021-9606. doi:10.1063/1.1561434.

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Ultrafast dissociation and recombination dynamics of (O_2)^−_n, n=3–10 was studied using femtosecond,time-resolvedphotoelectron spectroscopy. The observed transients of nascent fragment anions, following 800 nm fs pulse excitation, exhibit a biexponential rise with two distinct time constants. The time constants, which vary with the number of solvent O_2 molecules, clearly show the solvation effect in two different dissociation pathways. Consistent with the bifurcation picture in the preceding paper, the direct subpicosecond dissociation(τ_1=110-620 fs, depending on n) is governed by electron recombination and kinematics of the half-collision. The second pathway is indirect (τ_2=0.7–8.0 ps, for O^−_6 to O^−_(20)) and controlled by intramolecular vibrational-energy redistribution. In the solvent cage, only O^−_(16), O^−_(18), and O^−_(20) show the reformation of the bond, with the caging time constant decreasing from 4 ps for the first two to 2 ps for the latter. This caging through ion-induced dipole interaction is then followed by vibrational relaxation on the time scale of 12 to 3 ps, for O^−_(16) to O^−_(20). The time scale for the initial direct caging is two to five times slower than that previously observed for diatoms, neutral, or ionic, in van der Waals clusters. We suggest that this initial slower caging is due to the reorientation of O^−_2 and O_2 to acquire a proper geometry for O^−_4 bond reformation. In these finite-sized homogeneous clusters, we compare theory with experiment. We also found a correlation between the vertical detachment energy and n^(−1/3), for n in the range of 2–10, which allow for a connection between the mesoscopic structures and a bulk-type dielectric continuum, with an effective dielectric constant.

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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 the referee for the thorough reading of the two manuscripts and for helpful comments.
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Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Issue or Number:15
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Official Citation:Femtosecond dynamics of solvated oxygen anions. II. Nature of dissociation and caging in finite-sized clusters Nam Joon Kim, D. Hern Paik and Ahmed H. Zewail J. Chem. Phys. 118, 6930 (2003);
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ID Code:69723
Deposited By: Ruth Sustaita
Deposited On:18 Aug 2016 19:02
Last Modified:11 Nov 2021 04:18

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