Vibrational open-quotes spinclose quotes and description of a family of coupled quasi-degenerate vibrational states of a rigid molecule

The vibrational open-quotes spinclose quotes operator is introduced, which permits the full description of a family of coupled quasi-degenerate vibrational states of a rigid molecule. The quasi-degeneracy within this approach can be ascribed to the existence, for a major concentration to the examined intramolecular motion, of an extended symmetry group compared with the point symmetry group of the molecule. As a concrete example, the complete form of the effective Hamiltonian of a dyad of the A1 and E coupled vibrational states of the molecule with the C3v point symmetry group was obtained as the Taylor series over dynamic variables. 7 refs