Vibronic couplings involving ground state

For a more complete description of the vibronic levels associated with the Tig(A2 + E) electronic excited state, the wave functions Tj [Eq. f32)] must be augmented to include vibrational wave functions associated with all of the normal modes other than a = 2,5a, and 5e. Here we shall restrict our attention to just those vibronic levels derived from the vibrational modes a = 2,5a, and 5e. Assuming no vibronic couplings involving the ground electronic state of our model system, the rotatory strength of a transition between the lowest vibrational level of the ground electronic state and the j-th vibronic level of the Tjg (t2g + eg) coupled state may be written as... 

The vibronic theory of the RR effect distinguishes two major intensity enhancement mechanisms that play a dominant role in the RR spectra (i) Franck-Condon (FC) principle and (ii) Herzberg-Teller (FIT) vibronic coupling, which have quite different properties. The FC scattering mechanism involves displacement of the potential minima of the ground and excited electronic states along a vibrational normal... 

Direct calculation of the vibronic coupling matrix elements involved in PJT models is mathematically not easy and requires explicit knowledge of the many excited states, which is difficult to obtain. The calculation can be greatly simplified assuming that the excited state wavefunction jf/) differs from the ground state one IFq) by just a one-electron excitation, cpi -> cpj [20], In this case, we can approximate the force constant in state I by... 

At this point you may have wondered why we have always stated that it is the excited state which is subject to vibronic coupling, and not the ground state as well. As will become apparent in the next chapter, only certain types of activators can be used to prepare a phosphor. These involve cations which have a ground state, So. In this type of electron structure,... 

---