Internal instability of vibrational motion of a triatomic molecule: Classical approach

This study reports the manifestation of KAM theory in a simple triatomic mo lecule. Numerical examples are presented which show that for some Hamiltoni an systems monotonic increase in energy does not always lead to irregular b ehavior. The transition from the normal mode at low energy to a local mode at higher one preserves the tori for some initial conditions, but between t hese two well-defined states, there are strongly perturbed ones which revea l a significant presence of chaotic behavior.