Knowledge Bank

Rotational and rovibrational constants including the quadratic vibration-rotation interaction constants (the "$\gamma$"s), vibrationally-dependent quartic centrifugal distortion constants, and equilibrium hexic centrifugal distortion constants for general non-linear triatomic molecules as derived from fourth-order Rayleigh-Schrodinger perturbation theory (VPT4) are presented. The derived constants include all terms from the Watson Hamiltonian except for the pseudopotential. The resulting expressions are applied to a model molecular system, and issues such as vibrational resonance are discussed.