Vibronic interactions benzene

Vibrational analysis of the benzene phosphorescence bands indicates that the radiative activity is induced predominantly by e2g vibrations [155, 156]. A weak but observable activity of b2g vibrations has also been found [156, 155, 157]. By introducing spin-orbit- and vibronic coupling through second order perturbation theory Albrecht [158] showed that the vibronic interaction within the triplet manifold is responsible for the larger part of the phosphorescence intensity. This also follows from comparison of the vibrational structure in phosphorescence and fluorescence spectra [159]. The benzene phosphorescence spectrum in rigid glasses [155] reveals a dominant vibronic activity of... 

More numerous, however, are aromatic compounds with an effectively planar n system, the optical activity of which comes from chiral perturbations. Benzene derivatives such as phenylalanine (3) are particularly important. The Lb band of the benzene chromophore (A = 260 nm) is neither magnetically nor electrically allowed. The symmetry selection rule may be broken by vibronic interactions or due to substituents. The interpretation of the observed rotatory strength is not easy, but empirical sector rules have been proposed. (Cf. Charney, 1979 Pickard and Smith, 1990.)... 

It has been known for some time that hexatrienes can be formed by reaction of excited benzene molecules with solvent in a frozen glass (262-264). Some details of the mechanism of this process have been deduced by Simons and Smith (90). They propose that intermolecular vibronic interaction with solvent is a necessary but not sufficient requirement for production of hexatrienes in viscous media. The reaction is associated with radiationless decay of the triplet state rather than a bimole-cular reaction of triplet benzene with neighboring solvent molecules. Since radiationless decay constitutes intersystem crossing, the product of the reaction is also in the ground state. It is stressed by the authors that hexatrienes are not produced in fluid media or by nonphosphorescent benzene derivatives in which there is a rapid competing decay of the triplet state. 

In this article we have given an overview over our theoretical studies on tlie multi-mode multi-state vibronic interactions in the benzene cation and several of its fluoro derivatives. These are all associated with multiple conical intersections between the... 

Phosphorescence Spectra.—Luminescence from a low-lying triplet state of water368 has been reported. It has been shown that two long-lived emission systems in the biacetyl crystal described previously by Sidman and McClure (see ref. 368) are in fact due to impurities, and a complete analysis is presented of the true 3AU xAg phosphorescence. The zero-zero band in emission is found at 20 327 cm-1.135 A satisfactory account of the six characteristic bands in the phosphorescence spectrum of benzene has been given on the basis of pseudo-Jahn-Teller vibronic interactions between the lower 3Blu and 3Elu states in which two active vibrations in the pseudo-cylindrical approximation are considered.369 The phosphorescence spectra of anthracene,3700 coronene,8706 benzophenone in aqueous solution,371 pyrimidine derivatives,372 porphyrins,298 873 and crystalline charge-transfer complexes 374 have been reported. 

Benzene has a relatively low ionization potential (9.247 eV or 74580 cm ) so that all transitions from a2u and many from eig will lie beyond it and lead to super-excited states The second 1P ivas shown to belong to the highest filled o orbital It is not our intention to treat the spectrum of benzene in detail we merely used it as an example for the benefit of the non-initiated Reader as a simple MO + Rydberg scheme without energies, vibronic interactions, a electrons, and so on. Since the... 

Ddscher M, Koppel H, Szalay PG (2002) Multistate vibronic interactions in the benzene radical cation. I. Electronic structure calculations. J Chem Phys 117 2645-2656... 

In 1933 Herzberg and Teller demonstrated that certain electronic transitions which are forbidden in the fixed nuclei approximation may attain a non-zero transition probability through the interaction of electronic and nuclear motions. What they essentially did was to note that in every molecule there exist asymmetric nuclear displacements which yield a non-zero expectation value for the gradient of the nuclear-electronic coulombic energy terms. To illustrate their mode of thought we shall here give a pictorial outline of the calculation of such vibronic intensities in two systems of current interest aromatic compounds and transition metal complexes. For the sake of clarity we shall limit our discussion to the exemplary molecular systems of benzene and potassium titanium hexafluoride (KjTiFg). 

Figure 5 Population dynamics of the coupled X, B, and C electronic states of the benzene radical cation. The initial wavepacket is a Gaussian, located on the C state surface in the center of the Franck-Condon zone, (a) Time evolution of the C state population under the influence of the C-B vibronic coupling, excluding the interaction with the X state, (b) Electronic population of the C state (full line), B state (dotted line), and X state (dashed line) as resulting from a quantum-dynamical three-state four-mode treatment, (c) Same as panel (b), but with inclusion of a fifth vibrational mode (C-C stretching mode)...

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