An internal coordinate model for molecular vibrations: the energy levels of H2O and H2S and related isotopic molecules

Refinement of a previously described model for describing the anharmonic vibrations of polyatomic molecules is presented. The nonlinear molecules XY2 (H2O, D2O, H2S, D2S) are used as examples and it is shown that quite good agreement with the observed spectrum can be obtained for the first twenty vibrational excitations with a six parameter potential function. Apart from its relative simplicity, the main improvement over previously reported work is the inclusion of the bending vibration within the formalism and refinement of the form of potential. It is pointed out that the model is readily extendable to the vibrational analysis of larger molecules. (author)