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Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer

Herek, J. L. and Pedersen, S. and Bañares, L. and Zewail, A. H. (1992) Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer. Journal of Chemical Physics, 97 (12). pp. 9046-9061. ISSN 0021-9606. http://resolver.caltech.edu/CaltechAUTHORS:HERjcp92

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Abstract

The real-time dynamics of hydrogen-atom-transfer processes under collisionless conditions are studied using femtosecond depletion techniques. The experiments focus on the methyl salicylate system, which exhibits ultrafast hydrogen motion between two oxygen atoms due to molecular tautomerization, loosely referred to as intramolecular ''proton'' transfer. To test for tunneling and mass effects on the excited potential surface, we also studied deuterium and methyl-group substitutions. We observe that the motion of the hydrogen, under collisionless conditions, takes place within 60 fs. At longer times, on the picosecond time scale, the hydrogen-transferred form decays with a threshold of 15.5 kJ/mol; this decay behavior was observed up to a total vibrational energy of approximately 7200 cm-1. The observed dynamics provide the global nature of the motion, which takes into account bonding before and after the motion, and the evolution of the wave packet from the initial nonequilibrium state to the transferred form along the O-H-O reaction coordinate. The vibrational periods (2pi/omega) of the relevant modes range from 13 fs (the OH stretch) to 190 fs (the low-frequency distortion) and the motion involves (in part) these coordinates. The intramolecular vibrational-energy redistribution dynamics at longer times are important to the hydrogen-bond dissociation and to the nonradiative decay of the hydrogen-transferred form.


Item Type:Article
Additional Information:Copyright © 1992 American Institute of Physics. Received 15 July 1992; accepted 9 September 1992. This work was supported by a grant from the Air Force Office of Scientific Research and by the National Science Foundation. We wish to thank Dr. R. M. Bowman for his initial help with the depletion experiments. We also thank Professors M. Okumura and W. Miller for helpful discussions.
Subject Keywords:HYDROGEN; FS RANGE; METHYL COMPOUNDS; SALICYLIC ACID; ION EXCHANGE; TUNNEL EFFECT; EXCITED STATES; POTENTIAL ENERGY SURFACES; DISSOCIATION; HYDROGEN BONDS; REAL TIME SYSTEMS; CHEMICAL REACTIONS
Record Number:CaltechAUTHORS:HERjcp92
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:HERjcp92
Alternative URL:http://dx.doi.org/10.1063/1.463331
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1857
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 Feb 2006
Last Modified:26 Dec 2012 08:46

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