Subject vibronic coupling

While the proceedings of the sixteenth conference went into press, news agencies around the world announced the decease of Dr. Edward Teller at the age of 95. The Jahn-Teller community commemorates him as author, together with Jahn, of the seminal paper that gave birth to the entire subject of symmetry breaking and vibronic coupling. 

Thus, with these proofs two important additions to the previous traditional understanding of the JTE emerged (1) Any polyatomic system may be subject to the JTE, and (2) if there are instabilities and distortions of high-symmetry configurations, they are due to, and only to the JTE. Together with the previously achieved understanding of the role of quadratic terms of the vibronic coupling, the extended formulation of the JTE that includes the latest achievements in this field is as follows [1,8] ... 

Ai (Ajg) + Ea(Tjg) transition. The Aig - Tig CD would not reflect any aspects of the A - A2 component of the Aig + Tig transition. This picture is altered drastically when vibronic coupling effects are taken into account. Vibronic coupling may enter into this problem in several ways. First, both the Tig and T2g states are subject to "intra-state" couplings of the types (for example) Tig (t2g + eg) and T2g (t2g + eg). Secondly, "inter-state" coupling of the type (Tig + T2g) (t2g + eg) may become important. We shall examine the possible influence of this latter ("interstate ) type of coupling here. 

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,... 

Vibronic coupling through a normal mode that is nontotally symmetric is subject to symmetry restrictions. Just as vibrational potentials must be even functions of nontotally symmetric coordinates, so vibronic coupling... 

Totally symmetric modes are not subject to symmetry restrictions. Their potentials may contain odd and even terms in Q so that the harmonic-oscillator approximation imposes unwarranted symmetry restrictions. Similarly, the corresponding vibronic coupling operator may contain both odd and even terms so that the distinction between pseudo-Jahn-Teller and pseudo-Renner-Teller coupling disappears. Since the potential energy minimum of a totally symmetric mode is different in different electronic states, the pseudo-Jahn Teller/Renner-Teller limit is quite different from the limiting cases discussed in Section I V,B,C. Finally, the transition moments... 

Thus far we have assumed that the electronic ground state itself is not involved in the vibronic coupling but simply serves as an inert probe for the coupling between excited states. If the ground state is subject to coupling through the mode being probed, complications arise that lead to modification of some of our previous conclusions. 

---