Lowest excited states structure

The first job step computes the energies of the three lowest excited states. The second job step uses its results to begin the optimization by including the Read option to the CIS keyword, Geom=Check, and Guess=Read (and of course the commands to name and save the checkpoint file). The Freq keyword computes the frequencies at the optimized structure. 

In a regime of strong interaction between the chains no optical coupling between the ground slate and the lowest excited state occurs. The absence of coupling, however, has a different origin. Indeed, below 7 A, the LCAO coefficients start to delocalize over the two chains and the wavefunclions become entirely symmetric below 5 A due to an efficient exchange of electrons between the chains. This delocalization of the wavcfunclion is not taken into account in the molecular exciton model, which therefore becomes unreliable at short chain separations. Analysis of the one-electron structure of the complexes indicates that the... 

It has been empirically known that the energies of the lowest excited state of tetrahedrally coordinated metals decrease in the order Cr + < Mn + < Fe ". As in the case of 3cf elements, this tendency has been considered to originate from the difference in covalency, which reduced two-electron repulsion between the electrons occupying 3d orbitals. Recently this question was treated using first-principles electronic-structure calculation (Ishii et al. 2002). The same tendencies were found as for the 3d ions. Distance dependent multiplet-energy diagrams for these elements have been obtained (Fig. 5.34), which enable us to envisage the typical shapes of the possible emissions. As in... 

An unresolved puzzle remains22 the first two vibrational peaks in the first band in the photoelectron spectrum are separated only by 360 20 cm4, less than the lowest frequency vibration observed in neutral propellane (529 cm4), and very much less than its lowest totally symmetric vibration (908 cm 1). Yet, the authors calculations22 suggest that the lowest frequency totally symmetrical vibration of the radical cation will be at higher and not lower frequencies. The authors suggested that the vibrational structure may be due to vibronic mixing with the lowest excited state of the radical cation. 

Fig. 4 Energy correlation diagram between the gas phase (/G) and solvated (toluene) (/S) lowest excited states in a TFB F8BT model system calculated by TD-DFT (B3LYP/6-31G(d)). The eclipsed vs. staggered structures as shown in Fig. 3 are compared. The lowest-lying excitonic (XT) and charge transfer (CT) states are highlighted in red. Solvation effects tend to stabilize the CT state. Reprinted with permission from Ref. [41]. Copyright 2007, American Institute of Physics.

In the following we will first discuss examples of polytriacetylenes (Fig. 19) and then compare these results with the ones of other molecular structures. Monomers of poly triacetylenes with the three neutral end groups TMS (trimeth-ylsilyl), TES (triethylsilyl), and TIPS (triisopropylsilyl) have been investigated. By deconvolution of the absorption spectra assuming Gaussian fine shapes the wavelengths A00 for the absorption process from the ground state to the zero vibrational mode of the lowest excited state are obtained as described below. 

The lowest excited state of most ketones has the (n, n ) electronic structure, which gives the carbonyl (C=0) double bond a 1,2-biradical character. Therefore, the electron-deficient oxygen atom of this moiety, obtained upon excitation, acquires a radical reactivity, similar to the alkoxy radical. This excited state property of ketones leads to intramolecular H-abstraction to form 1-hydroxy-l, x-biradicals. Depending upon the structure and reaction conditions of the carbonyl compound, two common competing reactions may follow ... 

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