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S1/S2 excitonic splittings and vibronic coupling in the excited state of the jet-cooled 2-aminopyridine dimer.
- Source :
-
Journal of Chemical Physics . 11/28/2009, Vol. 131 Issue 20, p204308. 11p. 3 Diagrams, 4 Charts, 7 Graphs. - Publication Year :
- 2009
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Abstract
- We analyze the vibronic band structure of the excitonically coupled S1←S0/S2←S0 excitations of the 2-aminopyridine (2AP) self-dimer (2AP)2, using a linear vibronic coupling model [R. Fulton and M. Gouterman, J. Chem. Phys. 41, 2280 (1964)]. The vibronic spectra of supersonically cooled (2AP)2 and its 13C-isotopomer were measured by two-color resonant two-photon ionization and UV/UV-depletion spectroscopies. In the C2-symmetric form of (2AP)2, the S1←S0 (1A←1A) transition is very weak, while the close-lying S2←S0 (1B←1A) transition is fully allowed. A single 12C/13C isotopic substitution breaks the symmetry of the dimer so that the (2AP)2-13C isotopologue exhibits both S1 and S2 electronic origins, which are split by 11 cm-1. In Fulton–Gouterman-type treatments, the linear vibronic coupling is mediated by intramolecular vibrational modes and couplings to intermolecular vibrations are not considered. For (2AP)2, a major vibronic coupling contribution arises from the intramolecular 6a′ vibration. However, the low-energy part of the spectrum is dominated by intermolecular shear (χ′) and stretching (σ′) vibrational excitations that also exhibit excitonic splittings; we apply a linear vibronic coupling analysis for these also. The respective excitation transfer integrals VAB are 50%–80% of that of the intramolecular 6a′ vibration, highlighting the role of intermolecular vibrations in mediating electronic energy exchange. The S1/S2 electronic energy gap calculated by the approximate second-order coupled-cluster method is ∼340 cm-1. This purely electronic exciton splitting is quenched by a factor of 40 by the vibronic couplings to the Franck–Condon active intramolecular vibrations. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219606
- Volume :
- 131
- Issue :
- 20
- Database :
- Academic Search Index
- Journal :
- Journal of Chemical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 45515306
- Full Text :
- https://doi.org/10.1063/1.3266937