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Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls

Park, Sang Tae and Feenstra, Jonathan S. and Zewail, Ahmed H. (2006) Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls. Journal of Chemical Physics, 124 (17). Art. No. 174707. ISSN 0021-9606. https://resolver.caltech.edu/CaltechAUTHORS:PARjcp06

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Abstract

The photophysics and photochemistry of molecules with complex electronic structures, such as aromatic carbonyls, involve dark structures of radiationless processes. With ultrafast electron diffraction (UED) of isolated molecular beams it is possible to determine these transient structures, and in this contribution we examine the nature of structural dynamics in two systems, benzaldehyde and acetophenone. Both molecules are seen to undergo a bifurcation upon excitation (S2). Following femtosecond conversion to S1, the bifurcation leads to the formation of molecular dissociation products, benzene and carbon monoxide for benzaldehyde, and benzoyl and methyl radicals for acetophenone, as well as intersystem crossing to the triplet state in both cases. The structure of the triplet state was determined to be "quinoidlike" of * character with the excitation being localized in the phenyl ring. For the chemical channels, the product structures were also determined. The difference in photochemistry between the two species is discussed with respect to the change in large amplitude motion caused by the added methyl group in acetophenone. This discussion is also expanded to compare these results with the prototypical aliphatic carbonyl compounds, acetaldehyde and acetone. From these studies of structural dynamics, experimental and theoretical, we provide a landscape picture for, and the structures involved in, the radiationless pathways which determine the fate of molecules following excitation. For completeness, the UED methodology and the theoretical framework for structure determination are described in this full account of an earlier communication [J. S. Feenstra et al., J. Chem. Phys. 123, 221104 (2005)].


Item Type:Article
Related URLs:
URLURL TypeDescription
http://scitation.aip.org/content/aip/journal/jcp/124/17/10.1063/1.2194017PublisherArticle
http://dx.doi.org/ 10.1063/1.2194017OtherUNSPECIFIED
http://dx.doi.org/ 10.1063/1.2194017OtherUNSPECIFIED
Additional Information:© 2006 American Institute of Physics. Received: 23 February 2006; accepted: 14 March 2006; published online: 4 May 2006. We would like to thank the National Science Foundation and the Air Force Office of Scientific Research for providing support for this work. We would also like to thank Dr. Shoujun Xu for his assistance in the design of the sample inlet.
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Funding AgencyGrant Number
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Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Subject Keywords:EXCITATION-ENERGY DEPENDENCE; PHOSPHORESCENCE QUANTUM YIELD; PI-PI-ASTERISK; TRIPLET-STATES; GAS-PHASE; MOLECULAR-STRUCTURES; BENZALDEHYDE VAPOR; PHOTO-IONIZATION; PHOTOELECTRON-SPECTROSCOPY; RADIATIONLESS TRANSITIONS
Issue or Number:17
Record Number:CaltechAUTHORS:PARjcp06
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:PARjcp06
Official Citation:Ultrafast electron diffraction: Excited state structures and chemistries of aromatic carbonyls Park, Sang Tae and Feenstra, Jonathan S. and Zewail, Ahmed H., The Journal of Chemical Physics, 124, 174707 (2006), DOI:http://dx.doi.org/10.1063/1.2194017
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3618
Collection:CaltechAUTHORS
Deposited By: Lindsay Cleary
Deposited On:21 Jun 2006
Last Modified:02 Oct 2019 23:05

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