ABSTRACT
Spectroscopic techniques such as the dispersed fluorescence, and stimulated emission pumping have revealed a new dynamical picture of small polyatomic molecules excited at very high vibrational states. The established theoretical methods based on a normal mode description of the molecular vibrations, applied at energies close to the equilibrium point, are not any longer valid for vibrationally excited molecules. Periodic orbits evolve with the energy of the system or any other parameter in the Hamiltonian, bifurcate and produce new periodic orbits which portrait the resonances among the vibrational degrees of freedom. Bifurcation phenomena that is the change of the structure of the orbits by varying one or more parameters, are well known in vibrational spectroscopy. Periodic orbits which emerge from saddle-node bifurcations appear abruptly at some critical value of the energy, usually in pairs, and penetrate in regions of nuclear phase space where the normal mode motions can not reach.
