Charge resonance bands

To the best of our knowledge, pulse radiolysis transient absorption studies of neat CS2 have not been reported. CS2 anion in 0.1 M cyclohexane and 0.1 M THF solutions appears as a single 275-nm peak [35] there is no charge-resonance band that can be attributed to the dimer anion, at early (< 10 nsec) or later times. 

D. Charge Resonance Band in the Near-Infrared Region and Ultrafast Dynamics for Styrylpyridinium Tetraphenylborate Salts... 

Table III shows that at SA separation, the excitations nicely classify as either excitonic or charge resonance (the combination of two charge transfer excitations that exactly cancel any net charge transfer in the state.). As shown in Table III, this is not the case for the system at 3.5 A. We note that at the sA separation there is a small splitting of 300 cm. of the two excitonic bands, and no calculated splitting of the two charge resonance bands calculated some 3,700 cm. higher in energy. From the Cl coefficients after projection the two lowest bands, Qyl and Qy2, are pure excitonic, the two higher, Qy3 and Qy4, pure charge resonance.

Fig. 10 Electronic absorption spectra for the radical cations [(t-BuC02)3MM]2(p,-02CC2)" ", where MM = M02, MoW, and W2, showing the IVCT/charge resonance bands inTHF solution at...

The electron-transfer rate constant of the C q-PVCz system is larger than the system of Qo and Af-ethylcarbazole (EtCz) when Cgg is excited by the 532-nm laser, although EtCz corresponds to the unit structure of PVCz. The larger rate constant of PVCz can be attributed to the stable radical cation of PVCz due to the stacking of the carbazole moieties in the polymer chain as observed by the charge-resonance band in the near-IR region of the transient absorption spectra. The effect of the stacking of the carbazole moieties on the electron-transfer rate constants was discussed on the basis of the data on the electron-transfer processes between Cgg and various carbazole dimer models (Fig. 8) [57]. It has been confirmed that electron transfer proceeds effectively with the fuUy stacked carbazole dimers which stabilize the radical cations effectively. 

Cycloreversion of TPCB" and dimerization of St are summarized in Scheme 3, in which TT-(t-St)2, cr-St2, and the t-St /t-St pair are involved as the key intermediates. ir-(t-St)2 takes various overlapping arrangements of the rr-electrons between two benzene rings, and exhibits a large charge resonance (CR) band at shorter X of 680-800 nm than those of other dimer reported [84], On the other hand, a-St 2 has an acyclic linear structure. 

It was noted earlier that the charge density of a narrow resonance band lies within the atoms rather than in the interstitial regions of the crystal in contrast to the main conduction electron density. In this sense it is sometimes said to be localized. However, the charge density from each state in the band is divided among many atoms and it is only when all states up to the Fermi level have contributed that the correct average number of electrons per atom is produced. In a rare earth such as terbium the 8 4f electrons are essentially in atomic 4f states and the number of 4f electrons per atom is fixed without reference to the Fermi level. In this case the f-states are also said to be locaUzed but in a very different sense. Unfortunately the two senses are often confused in literature on the actinides and, in order not to do so here, we shall refer to resonant states and Mott-localized states specifically. 

Excimer may relax (i) by emission of characteristic structureless band shifted to about 6000 cm-1 to the red of the normal fluorescence, (ii) dissociate nonradiatively into original molecules, (iii) form a photodimer. Those systems which give rise to photodimers may not decay by excimer emission. The binoing energy for excimer formation is provided by interaction between charge transfer (CT) state A+A- A-A and charge resonance state AA s A A. 

What is the nature of the excimer bond Quantum mechanical calculations of the theoretical position of excimer fluorescence bands give good agreement with experimental positions if excitation resonance and charge resonance are both taken into account—that is, if the structure of the excimer is described by Equation 13.26.33... 

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