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Photodissociation of Bromobenzene, Dibromobenzene, and 1,3,5-Tribromobenzene
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
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2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 14, 6502- p.Article in journal (Refereed) Published
Abstract [en]

Quantum chemical calculations have been performed on the ground state and several low-lying excited states of bromobenzene, ortho-, meta-, and para-dibromobenzene, and 1,3,5-tribromobenzene using high-level ab initio and hybrid density-functional methods. Experimental observations of ultrafast predissociation in these molecules are clarified from extensive theoretical information about all low-energy potential-energy curves together with symmetry arguments. The intriguing observation that o- and m-dibromobenzene have two ultrafast predissociation channels while bromobenzene, p-dibromobenzene, and 1,3,5-tribromobenzene only have one such channel is explained from the calculated potential-energy curves. These show that the lowering of point-group symmetry from C2v to Cs along the main photodissociation reaction coordinate, which only occurs in o- and m-dibromobenzene, opens up a new predissociation channel. Dynamical quantum simulations based on the calculated potential-energy curves are used to estimate the coupling strength at the intersystem crossing point in bromobenzene.

Place, publisher, year, edition, pages
2004. Vol. 120, no 14, 6502- p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96968DOI: 10.1063/1.1667460OAI: oai:DiVA.org:uu-96968DiVA: diva2:171721
Available from: 2008-04-02 Created: 2008-04-02 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Photochemistry of Phenyl Halides
Open this publication in new window or tab >>Photochemistry of Phenyl Halides
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We have studied fundamental aspects of photo-induced dissociation kinetics and dynamics in several phenyl halides. By combining femtosecond pump-probe measurements with ab initio calculations we are able to account for several observations. In mixed phenyl halides, the dissociation kinetics is found to be dependent on the nature, the number, and the position of the substituents, and also on the excitation wavelength. A surprisingly large reduction in the dissociation time constant, compared to that of bromobenzene (~30 ps), is observed when having two or more fluorine atoms. For example, in bromopentafluorobenzene a subpicosecond time constant is obtained. This can be explained by a significant lowering of the repulsive potential energy curves (PEC) along the C-Br bond. However, several of the experimental results cannot be accounted for by one-dimensional PECs. Therefore, we suggest a refined model for the dissociation, in which the excited states of the same spin multiplicity are coupled by employing multidimensional potential energy surfaces. This model has been explicitly evaluated by quantum dynamics simulations in the case of 3-BrFPh, and it seems to be capable of capturing the main features in the measured kinetics. Thereby we are also able to clarify the role of spin-orbit coupling in these molecules.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 57 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 417
Keyword
Chemistry, Photochemistry, Predissociation, Phenyl halides, Excited states, Substituent effects, Pump-probe spectroscopy, Molecular beam, Dynamics, Kemi
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-8602 (URN)978-91-554-7146-0 (ISBN)
Public defence
2008-04-24, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Available from: 2008-04-02 Created: 2008-04-02 Last updated: 2011-03-14Bibliographically approved

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Karlsson, Hans O.

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