Nondegenerate single excited state

Variational Theory for a Nondegenerate Single Excited State. 125... 

VARIATIONAL THEORY FOR A NONDEGENERATE SINGLE EXCITED STATE... 

As stated in the preceding section, it is sufficient to consider only singly excited states in the Cl treatment. For the simplest case, where the ground-state configuration has one nondegenerate singly occupied MO, the types of singly excited states are presented in Fig. 1 and the respective wave functions can be expressed as follows... 

Thus in crystals where unit cells contain a molecules, to any single nondegenerate excited state of a free molecule in the crystal corresponds not one, but a bands of excited states and correspondingly several absorbtion lines. Such a splitting was first discussed by Davydov ((9)—(11)) and is usually called the Davydov splitting,8 to distinguish it from the Bethe splitting (14). 

In the four-orbital model (1 ), low-lying ir-ir states of free-base porphyrins (symmetry D2h) are considered as resulting from single electron excitation from a pair of nondegenerate highest occupied molecular orbitals (bi, bo) to a pair of nondegenerate lowest unoccupied molecular orbitals (ci, cg). In the case of symmetry D2h mutually perpendicular electric transition dipoles X and Y are not equivalent and, therefore, in the visible absorption spectra of free-base porphyrins two different electronic bands Qx(0>0) and Qy(0,0) are observed (Table 1 and Fig. 10). 

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