Potential energy function of polyatomic molecules: Automatic determination of the unitary transformation operator for the perturbation treatment of the Hamiltonian

Abstract

An original method for the automatic determination of the unitary transformation operator that occurs in the Van Vleck's perturbation method is presented for the case of the vibrational Hamiltonian of linear triatomic molecules. This method is a general one and may be applied to the vibro-rotational Hamiltonian of more complicated molecules even when one or several rotational resonances occur simultaneously with one or several vibrational resonances. Numerical results are given for the case of CO 2 (vibrational Hamiltonian). The computation time is discussed.