Singlet state, minimum energy

Figure 11-7. Minimum energy pathways on the Si surface of cytosine connecting the Si minimum to two Si/So conical intersections. The five singlet state energies at the MRCI level are shown. Energies are given in eV with respect to the ground state minimum energy, ciIJ represents conical intersection between states S/, Sj. (From Ref. [157])...

The isomerization of alkenes is believed to take place via an excited state in which the two sp carbons are twisted 90° with respect to one another. This state is referred to as the p (perpendicular) state. This geometry is believed to be the minimum-energy geometry for both the singlet and triplet excited states. 

Table 11-1. Vertical excitation energies in eV relative to the ground state minimum of the singlet electronic excited states in the uracil...

Direct conversion systems are threshold devices, that is, there is a minimum photon energy which can initiate the photochemical reaction. This is called the band-gap ei rgy Eg with a corresponding band-gap wavelength Xg. Eg usually corresponds to the 0-0 transition to the lowest excited singlet state of the absorber (see Fig. 1). Hence, it is important to know what fraction of the incident solar power is available at the band-gap energy. 

It is important to note that for methyl nitrenium ion the singlet state is not predicted at higher levels of theory to show a potential energy minimum. Rather this species is a transition structure that eliminates H2 without a barrier (Fig. 13.15). It seems likely that the difficulties encountered in attempting to study alkyl nitrenium ions might be traced to their propensity to rearrange or eliminate. 

He found that the EE trimethylene species was associated with a shallow minimum on the singlet state energy surface, and that this intermediate structure could progress to the much deeper valley of cyclopropane most easily, surmounting an activation barrier of only... 

The energies of the planar ground and excited states are taken from the review of Saltiel et al. (1) and are summarized in Table 1. Isomerization of It and lc is presumed to occur via a common twisted intermediate Ip without intersystem crossing to the triplet manifold. The minimum is ascribed to either an avoided or allowed crossing of the first ( Bu ) and second (lAg ) excited singlet states (13). The fluorescent It state has a radiative lifetime of 1.7- 2.7 ns. A barrier of... 

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