Assigning the transition from normal to local vibrational mode in SO2 by periodic orbits

The bifurcation diagrams of periodic orbits are compared for three different potential functions of the ground electronic state of SO2. By assigning families of periodic orbits to overtone and combination vibrational levels of the symmetric stretch mode, the transition from normal- to local-type motions is identified to take place at the energy where the symmetric stretch family turns from stable to unstable and new local-type periodic orbits are generated.