Theoretical Approaches to Anharmonic Resonances

Four theoretical models for the treatment of anharmonic resonances are discussed, and one particular curvilinear approach is generalized. Theoretical resonance parameters for three of these models are calculated on the basis of ab initio anharmonic force fields. They are compared with experimentally derived effective resonance parameters and with other published theoretical data. 25 anharmonic resonances in 16 different molecules are covered, including the stretch-bend Fermi resonances in the haloforms CHX3 and the methyl halides CH3X(X = F-I). These comparisons suggest guidelines for the theoretical treatment of resonances