A Modified Vibron Model for Anharmonic Vibrations: Application to Rovibrational Levels of Linear XYZ and XY(2)...

The vibron model for anharmonic vibrations of simple polyatomic molecules has been modified by explicit inclusion of the bending energy in the vibron hamiltonian, and by incorporating vibrationally and rotationally dependent terms into the main parameters of the model. These modifications keep the simple form of the basic vibron energy expressions unchanged but make them far more flexible and capable of much higher precision than those of the pure algebraic vibron model, even one with all squares and binary products of the Casimir operators included. Applications of the modified equations to the vibrational levels and rovibrational energies of the linear molecules HCN, CO(2), and some of their isotopomers show that this modified model yields precision of fitting which is better by one to two orders of magnitude than that provided by the strict algebraic model. This suggests that the modified vibron model can provide a simple but useful alternative to the much more elaborate global treatments of the rovibrational data. Copyright 2000 Academic Press.