Lowest extended states

Regarding the emission properties, AM I/Cl calculations, performed on a cluster containing three stilbene molecules separated by 4 A, show that the main lattice deformations take place on the central unit in the lowest excited state. It is therefore reasonable to assume that the wavefunction of the relaxed electron-hole pair extends at most over three interacting chains. The results further demonstrate that the weak coupling calculated between the ground state and the lowest excited state evolves in a way veiy similar to that reported for cofacial dimers. 

If e is now decreased, with the chain in the extended state, the dumbbell nevertheless stays in the stretched state where the potential is the lowest. The transition back to the coiled state occurs only when there is a single minimum on the potential energy curve, i.e. at et = 0.15. Since the critical strain-rate for the stretch-to-coil transition (esc) is much below the corresponding value for the coil-to-stretch transition (eca), the chain stretching phenomenon shows hysteresis (Fig. 11). 

The variation method is usually employed to determine an approximate value of the lowest eneigy state (the ground state) of a given atomic or molecular system. It can, furthermore, be extended to the calculation of energy levels of excited stales. It forms the basis of molecular orbital theory and that which is often referred to (incorrectly) as theoretical chemistry". 

Comparison of the computed and the measured relative cross sections between 575 and 630 nm shows a difference which is indicative for the lowest triplet state of a riboflavin. The action spectrum has a small peak at 595 nm and a cutoff at 585 nm and a tail extending beyond 630 nm. The peak at 595 nm may be regarded, within the accuracy of this system, as the lowest triplet state of riboflavin and can be compared to the value of 600 nm obtained by phosphorescence emission for this state (Song and Moore, 1974). 

The extended model has been subjected to a number of tests. Without any parameter adjustments, the model reproduces the energie and B(E2) values of the lowest 2 states of doubly magic nuclei. 

Re and 7e specify the equilibrium of the electronic ground state and the exponents an and o 7 are related to the frequencies according to (5.16). Throughout this section we will assume that the parent molecule is in its lowest bending state before the excitation takes place. The summation in (6.22) extends over all trajectories which start with initial angle 70O ) and end with a specified final angular momentum j, i.e., which solve the... 

Table 10.20. Potential curves (in Hartrees) for the five lowest electronic states of CH, calculated by Lie, Hinze and Liu [188] using an extended configuration interaction method...

Nanosecond time-resolved resonance Raman and absorption spectra of 6-nitroBIPS in deoxygenated cyclohexane were obtained in the 20-100-ns time region, extending an earlier study169 in the 200-2000-ns time region. A sequence of three transients was observed (1) the lowest triplet state 7i, X 435 nm, of the spiro form (2) the open merocyanine form, X 580 nm, formed from the triplet (1) and (3) a dimer of the merocyanine, X 540 nm.170... 

Examples of the low temperature luminescence spectra are shown in Fig. 8.12. The luminescence intensity is highest in samples with the lowest defect density and so we concentrate on this material. The role of the defects is discussed in Section 8.4. The luminescence spectrum is featureless and broad, with a peak at 1.3-1.4 eV and a half width of 0.25-0.3 eV. It is generally accepted that the transition is between conduction and valence band tail states, with three main reasons for the assignment. First, the energy is in the correct range for the band tails, as the spectrum lies at the foot of the Urbach tail (Fig. 8.12(6)). Second, the luminescence intensity is highest when the defect density is lowest, so that the luminescence cannot be a transition to a defect. Third, the long recombination decay time indicates that the carriers are in localized rather than extended states (see Section 8.3.3). 

The theoretical treatment of the dynamic Jahn-Teller effect in Li3 with the PNO-CEPA-CI ab initio method (25) has been refined in the groundstate and extended to the lowest four electronically excited states in the PNO-CI approximation(26,27). Two cross sections for the adiabatic hypersurfaces for the groundstate E and the lowest excited state, E",are shown in Figure 11. The flat groundstate surface exhibits a roughly triangular trough... 

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