Raman studies of diphenylhexatriene in the first excited singlet state evidence strong vibronic coupling between two close 1Bu/2Ag states. The geometrical change after photoexcitation contains a dominant contribution of a low-frequency mode with bu symmetry near 40 cm-1. This mode is identified as a relatively strong line in the Raman spectrum. Vibronic coupling mainly affects two C=C stretching Raman bands near 1700 cm-1. A two-dimensional effective potential for the lowest excited singlet state is derived which models the coupling between the coordinate of the 40 cm-1 mode and the C=C stretching coordinate, thereby explaining the occurrence of the two bands and their strong solvent shift. The model gives, in the zero gap limit, a double-well potential for the C=C stretching coordinate, due to the pseudo-Jahn-Teller effect. Modulation of this potential by the low-frequency cycle explains the spectral broadening observed in the Raman spectra.
|Original language||English (US)|
|Number of pages||7|
|Journal||Chemical Physics Letters|
|State||Published - Oct 2 1998|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Atomic and Molecular Physics, and Optics