Calculation of rovibrational spectra of water by means of particles-on-concentric-spheres models. II. Excited states of stretching vibrations

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Abstract
It is shown that adiabatic separation of high‐frequency stretching modes from bending and overall rotational motions in triatomic molecules XY2 leads naturally to the particles‐on‐a‐sphere (POS) model treated previously [J. Chem. Phys. 8 1, 3400 (1984)]. Solution of the rovibrational problem using a further approximation in which stretching motions are treated as uncoupled modes is then investigated in detail. It is shown that, for states with a significantly larger number of quanta in one bond than the other, the POS model in this approximation yields energy levels that are essentially identical with those for the particles‐on‐concentric‐spheres (POCS) model, where the latter is obtained using a different decoupling of the basic set of differential equations.