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Solvation Ultrafast Dynamics of Reactions. 8. Acid-Base Reactions in Finite-Sized Clusters of Naphthol in Ammonia, Water, and Piperidine

Kim, S. K. and Breen, J. J. and Willberg, D. M. and Peng, L. W. and Heikal, A. and Syage, J. A. and Zewail, A. H. (1995) Solvation Ultrafast Dynamics of Reactions. 8. Acid-Base Reactions in Finite-Sized Clusters of Naphthol in Ammonia, Water, and Piperidine. Journal of Physical Chemistry, 99 (19). pp. 7421-7435. ISSN 0022-3654. doi:10.1021/j100019a027.

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In this contribution, studies of the dynamics of proton-transfer reactions in solvent cages are presented, building on earlier work [Breen, J. J.; et al. J. Chem. Phys. 1990, 92, 805. Kim, S. K.; et al. Chem. Phys. Lett. 1994, 228, 369]. The acid-base system studied in a molecular beam is 1-naphthol as a solute and ammonia, piperidine, or water as the solvent, with the number of solvent molecules (n) varying. The rates and threshold for proton transfer have been found to be critically dependent on the number and type of solvent molecules: n = 2 for piperidine and n = 3 for ammonia; no proton transfer was observed for water up ton = 21. With subpicosecond time resolution, we observe a biexponential transient for the n = 3 cluster with ammonia. From these observations and the high accuracy of the fits, we provide the rate of the proton transfer at short times and the solvent reorganization at longer times. From studies of the effect of the total energy, the isotope substitution, and the number and type of solvent molecules, we discuss the nature of the transfer and the interplay between the local structure of the base solvent and the dynamics. The effective shape of the potential energy surface is discussed by considering the anharmonicity of the reactant states and the Coulombic interaction of ion-pair product states. Tunneling is related to the nature of the potential and to measurements specific to the isotope effect and energy dependence. Finally, we discuss a simple model for the reaction in finite-sized clusters, which takes into account the proton affinity and the dielectric shielding of the solvent introduced by the local structure.

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Additional Information:© 1995 American Chemical Society. Received: August 26, 1994; In Final Form: November 11, 1994. Abstract published in Advance ACS Abstracts, May 1, 1995. We are very happy to contribute this paper on the special occasion of Mostafa's 60th birthday (in the transition state to Georgia Tech). His scientific contributions and services are greatly appreciated, and we wish him many more years of productive and happy life-keep up the smile! We thank Professors P. M. Felker, E. R. Bernstein, and M. Okumura for helpful discussions. We also acknowledge the help of Drs. P. Cong, M. Gutmann, and J.-K. Wang during the different stages of this research. Finally, we thank the two referees for the thorough reading of the manuscript. This work is supported by a grant from the National Science Foundation.
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Arthur Amos Noyes Laboratory of Chemical Physics8979
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Official Citation:Solvation Ultrafast Dynamics of Reactions. 8. Acid-Base Reactions in Finite-Sized Clusters of Naphthol in Ammonia, Water, and Piperidine S. K. Kim, J. J. Breen, D. M. Willberg, L. W. Peng, A. Heikal, J. A. Syage, and A. H. Zewail The Journal of Physical Chemistry 1995 99 (19), 7421-7435 DOI: 10.1021/j100019a027
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69933
Deposited By: Ruth Sustaita
Deposited On:26 Aug 2016 15:45
Last Modified:11 Nov 2021 04:22

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