Computed overtone spectra of linear triatomic molecules by dynamical symmetry

The description of overtone states of linear triatomic molecules by an algebraic approach is discussed in detail. Applications to HCN, HCP, and OCS are provided. Emphasis is given to the separable limit ("the dynamical symmetry") where three good vibrational quantum numbers (and a vibrational angular momentum l) can be defined. Even in this limit, the vibrational modes are anharmonic. Resonance coupling of the Fermi and Darling-Dennison type is also discussed, both algebraically and computationally. The semiclassical limit of the Hamiltonian is used to obtain additional physical insight.