Bifurcation in the rotational spectra of nonlinear symmetric triatomic molecules

A microscopic theory is proposed for bifurcation in the rotational spectra of nonlinear AB2-type molecules. The theory is based on a study of small-amplitude vibrational and precessional motion near the stationary states of a rotating molecule. Bifurcation leads to the formation of fourfold clusters of levels in the upper parts of the rotational multiplets, disruption of the symmetry of the molecule, and a transition from normal to local valence vibrations. The role of the centrifugal force of inertia in the development of these effects is clarified. Bifurcation and the accompanying phenomena are studied in the hydride molecules H2O, H2S, H2Se, and H2Te using empirical molecular potentials.