Algebraic approach to molecular rotation-vibration spectra. II. Triatomic molecules

The algebraic approach to molecular rotation-vibration spectra introduced in a previous article is extended from di- to tri- and polyatomic molecules. The spectrum generating algebra appropriate to triatomic molecules U(4)⊗U(4) is explicitly constructed. Its dynamical symmetries and their relation to rigid, nonrigid, linear, and nonlinear structures are discussed. Applications to the spectra of HCN, CO2, and H+3 are considered. In particular, it is shown that the algebraic description can account for the Fermi resonances occurring in CO2. Some remarks are made on the spectrum generating algebras appropriate to polyatomic molecules.