Vibronic spectra case studies

The excited (Si) electronic state of BDO has been studied by Laane and coworkers [18] through the analysis of the vibronic spectrum measured in a supersonic jet laser spectrometer. They made a complete assignment of the vibronic structure of the spectrum, and, with the help of data from dispersed fluorescence and UV absorption in a cell, concluded that the molecule is nonplanar in both the So and the Si electronic states. Also in this case the anomeric effect was invoked in order to justify the nonplanarity due to the puckering of the five-membered ring and the butterfly motion of the two rings. 

Muller and Stock [227] used the vibronic coupling model Hamiltonian, Section III.D, to compare surface hopping and Ehrenfest dynamics with exact calculations for a number of model cases. The results again show that the semiclassical methods are able to provide a qualitative, if not quantitative, description of the dynamics. A large-scale comparison of mixed method and quantum dynamics has been made in a study of the pyrazine absorption spectrum, including all 24 degrees of freedom [228]. Here a method related to Ehrenfest dynamics was used with reasonable success, showing that these methods are indeed able to reproduce the main features of the dynamics of non-adiabatic molecular systems. 

T <- Tj spectrum shows a single peak at 235 nm F 0.35) and a shoulder around 310nm (F 0.12). Vibronic mechanisms in the two-photon spectrum of benzene and also toluene, halobenzenes, and aniline have been studied by Goodman and co-workers. Two-photon excitation of benzene crystals at 4.2 K has been recorded in the 200 nm second absorption system. The data suggest that the transition is in which the vibronic intensity is derived from the state in the one photon and E g in the case of two-photon excitation. Spectral solvent effects on toluene have been reported by Macovei. Traverso and Brunet have examined the 5j Sq transition in biphenyl and confirmed the earlier conclusion that this is a forbidden process. 

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