Raman dispersion spectroscopy on the highly saddled nickel(II)-octaethyltetraphenylporphyrin reveals the symmetry of nonplanar distortions and the vibronic coupling strength of normal modes
- FB1-Institute of Experimental Physics, University of Bremen, 28359 Bremen (Germany)
- Fuel Science Department, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
- Chemistry Department, University of Copenhagen, 5 Universitetsparken, DK-2100 Copenhagen (Denmark)
- Department of Chemistry, University of California, Davis, California 95616 (United States)
We have measured the polarized Raman cross sections and depolarization ratios of 16 fundamental modes of nickel octaethyltetraphenylporphyrin in a CS{sub 2} solution for 16 fundamental modes, i.e., the A{sub 1g}-type vibrations {nu}{sub 1}, {nu}{sub 2}, {nu}{sub 3}, {nu}{sub 4}, {nu}{sub 5}, and {phi}{sub 8}, the B{sub 1g} vibrations {nu}{sub 11} and {nu}{sub 14}, the B{sub 2g} vibrations {nu}{sub 28}, {nu}{sub 29}, and {nu}{sub 30} and the antisymmetric A{sub 2g} modes {nu}{sub 19}, {nu}{sub 20}, {nu}{sub 22}, and {nu}{sub 23} as function of the excitation wavelength. The data cover the entire resonant regions of the Q- and B-bands. They were analyzed by use of a theory which describes intra- and intermolecular coupling in terms of a time-independent nonadiabatic perturbation theory [E. Unger, U. Bobinger, W. Dreybrodt, and R. Schweitzer-Stenner, J. Phys. Chem. {bold 97}, 9956 (1993)]. This approach explicitly accounts in a self-consistent way for multimode mixing with all Raman modes investigated. The vibronic coupling parameters obtained from this procedure were then used to successfully fit the vibronic side bands of the absorption spectrum and to calculate the resonance excitation profiles in absolute units. Our results show that the porphyrin macrocycle is subject to B{sub 2u}-(saddling) and B{sub 1u}-(ruffling) distortions which lower its symmetry to S{sub 4}. Thus, evidence is provided that the porphyrin molecule maintains the nonplanar structure of its crystal phase in an organic solvent. The vibronic coupling parameters indicate a breakdown of the four-orbital model. This notion is corroborated by (ZINDO/S) calculations which reveal that significant configurational interaction occurs between the electronic transitions into {vert_bar}Q{r_angle}- and {vert_bar}1B{r_angle}-states and various porphyrin{r_arrow}porphyrin, metal{r_arrow}porphyrin, and porphyrin{r_arrow}metal transitions. (Abstract Truncated)
- Research Organization:
- Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 526878
- Journal Information:
- Journal of Chemical Physics, Vol. 107, Issue 6; Other Information: PBD: Aug 1997
- Country of Publication:
- United States
- Language:
- English
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