Dynamic Coupling Phenomena in Molecular Excited States. I. General Formulation and Vibronic Coupling H2
A general formalism is described for treating diabatic coupling processes in highly excited molecular states. The method treats electronic and nuclear motion quantum mechanically, and uses the adiabatic Born-Oppenheimer states as basis function. The present paper concentrates on diagnoses of vibronic coupling matrix elements, with Rydberg and continuum states of H2 as the test cases. The principal contributions come from the excited electron's interactions with the oscillating finite monopole of the ion-molecule core. The electronic factors in the transition amplitudes are definitely dependent on internuclear distance, particularly in the cases of p and d states. The transition amplitudes accumulate their magnitudes over the full classically allowed range of internuclear distance, especially in the cases of s and p states. Specific application is made to vibronic coupling perturbations in pσ and pπ Rydberg states of H2.