Electronic states degenerate

Baer M, Yahalom A and Engelman R 1998 Time-dependent and time-independent approaches to study effects of degenerate electronic states J. Chem. Phys. 109 6550... 

Non-adiabatic coupling is also termed vibronic coupling as the resulting breakdown of the adiabatic picture is due to coupling between the nuclear and electi onic motion. A well-known special case of vibronic coupling is the Jahn-Teller effect [14,164-168], in which a symmetrical molecule in a doubly degenerate electronic state will spontaneously distort so as to break the symmetry and remove the degeneracy. 

If the states are degenerate rather than of different symmetry, the model Hamiltonian becomes the Jahn-Teller model Hamiltonian. For example, in many point groups D and so a doubly degenerate electronic state can interact with a doubly degenerate vibrational mode. In this, the x e Jahn-Teller effect the first-order Hamiltonian is then [65]... 

PERMUTATIONAL SYMMETRY AND THE ROLE OF NUCLEAR SPIN IN THE VIBRATIONAL SPECTRA OF MOLECULES IN DOUBLY DEGENERATE ELECTRONIC STATES ... 

Now, we examine the effect of vibronic interactions on the two adiabatic potential energy surfaces of nonlinear molecules that belong to a degenerate electronic state, so-called static Jahn-Teller effect. 

The coupling of vibrational and electronic motions in degenerate electronic states of inorganic complexes, part 1 state of double degeneracy. A. D. Liehr, Prog. Inorg. Chem., 1962, 3, 281-314 (25). 

The two cases considered thus far have involved reactants in spatially non-degenerate electronic states. A significant new level of complexity is introduced in the termolecular association reaction,... 

Much of the success in the use of ion-molecule reactions to study SIKIE stems from the relative ease with which the theoretically identified requirement of there being identical reactants in different electronic states, or at least one of the reactants being in a degenerate electronic state, can be experimentally realized. Thus, it is natural to consider possible future directions in which ion-molecule studies might extend the current understanding of SIKIE. Presently, all known systems exhibiting... 

Jahn, H. A., and E. Teller Stability of polyatomic molecules in degenerate electronic states. I. Orbital degeneracy. Proc. Roy. Soc. A161, 220 (1937). 

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