Vibronic coupling effects in magnetic vibrational circular dichroism. A model formalism for doubly degenerate states

A formalism for magnetic vibrational circular dichroism (MVCD) of a model system is developed by considering vibronic coupling effects between a nondegenerate ground state and a degenerate excited state. Only one degenerate vibrational coordinate and one degenerate electronic excited state are considered in the model. A diabatic basis set representation was used for the vibronic functions paralleling previous Jahn–Teller effect formalisms. The parametrized model which results is shown to give MVCD A and B terms of a magnitude comparable to those previously observed for substituted benzenes. These model studies are suggestive that vibronic coupling effects are important for complete interpretation of MVCD spectra.