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Role of Electronic Curve Crossing of Benzene S-1 State in the Photodissociation of Aryl Halides, Effect of Fluorination: RASSI-SO MS-CASPT2 Study

Devarajan, Ajitha LU ; Gaenko, Alexander LU ; Lindh, Roland LU and Malmqvist, Per-Åke LU (2009) In International Journal of Quantum Chemistry 109(9). p.1962-1974
Abstract
An ab initio study of the role of electronic curve crossing of benzene S-1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low-lying n-sigma*, pi-sigma*, pi-pi* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene pi-pi* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low-lying... (More)
An ab initio study of the role of electronic curve crossing of benzene S-1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low-lying n-sigma*, pi-sigma*, pi-pi* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene pi-pi* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low-lying n-sigma*, pi-sigma*, pi-pi* states were studied including spin-orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI-MS-CASPT2) method. Crossing behavior of spin-free and spin-orbit potential energy curves was analyzed for the role of the benzene S-1 state. Our results indicate the curve crossing region to be around 2.00-2.35 angstrom for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene pi-pi* and n-sigma* transitions suggests an increase in the energy of benzene pi-pi* states and a decrease in the energy of the states corresponding to n-sigma* transitions. Increased spin-orbit gap, increased separation of the benzene S-1(pi-pi*) state and n-sigma* states in the region of curve crossing, lesser mixing of the pi-pi* and n-sigma* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed Substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1962-1974, 2009 (Less)
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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
spin-orbit, relativistic, multireference, ab initio, crossing, electric curve, C6F5I, photodissociation dynamics, Iodobenzene, MS-CASPT2, RASSI-SO, DHH
in
International Journal of Quantum Chemistry
volume
109
issue
9
pages
1962 - 1974
publisher
John Wiley & Sons Inc.
external identifiers
  • wos:000266179300019
  • scopus:67649842077
ISSN
0020-7608
DOI
10.1002/qua.22033
language
English
LU publication?
yes
additional info
The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Theoretical Chemistry (S) (011001039)
id
23112706-98a6-4d9b-9497-fdb29ee5cb44 (old id 1425642)
date added to LUP
2016-04-01 12:31:43
date last changed
2023-01-03 17:54:38
@article{23112706-98a6-4d9b-9497-fdb29ee5cb44,
  abstract     = {{An ab initio study of the role of electronic curve crossing of benzene S-1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low-lying n-sigma*, pi-sigma*, pi-pi* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene pi-pi* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low-lying n-sigma*, pi-sigma*, pi-pi* states were studied including spin-orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI-MS-CASPT2) method. Crossing behavior of spin-free and spin-orbit potential energy curves was analyzed for the role of the benzene S-1 state. Our results indicate the curve crossing region to be around 2.00-2.35 angstrom for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene pi-pi* and n-sigma* transitions suggests an increase in the energy of benzene pi-pi* states and a decrease in the energy of the states corresponding to n-sigma* transitions. Increased spin-orbit gap, increased separation of the benzene S-1(pi-pi*) state and n-sigma* states in the region of curve crossing, lesser mixing of the pi-pi* and n-sigma* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed Substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides. (c) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 1962-1974, 2009}},
  author       = {{Devarajan, Ajitha and Gaenko, Alexander and Lindh, Roland and Malmqvist, Per-Åke}},
  issn         = {{0020-7608}},
  keywords     = {{spin-orbit; relativistic; multireference; ab initio; crossing; electric curve; C6F5I; photodissociation dynamics; Iodobenzene; MS-CASPT2; RASSI-SO; DHH}},
  language     = {{eng}},
  number       = {{9}},
  pages        = {{1962--1974}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{International Journal of Quantum Chemistry}},
  title        = {{Role of Electronic Curve Crossing of Benzene S-1 State in the Photodissociation of Aryl Halides, Effect of Fluorination: RASSI-SO MS-CASPT2 Study}},
  url          = {{http://dx.doi.org/10.1002/qua.22033}},
  doi          = {{10.1002/qua.22033}},
  volume       = {{109}},
  year         = {{2009}},
}