A many‐body diagrammatic theory of rotation–vibration spectra

A many‐body diagrammatic perturbation theory of rotation–vibration spectra is elaborated. The present approach is based on two many‐body techniques, namely on the second quantization formalism (a rotating–vibrating molecule is formally treated here as a system of interacting vibrons, obeying the Bose–Einstein statistics) and the many‐body diagrammatic theory of a model Hamiltonian, initially suggested in the microscopic theory of nuclei and in the last decade very frequently exploited in the accounting for the correlation effects in many electron systems. In the framework of this theory, the rotation–vibration energies are determined as the eigenvalues of a finite‐dimensional model eigenproblem.