Nonlinear coupling between rotation and internal vibration in simple molecular systems

A Hamiltonian is proposed to describe the coupling between vibration and rotation in a molecular system. The time behaviour of such a system exhibits both regular and irregular motion for different energies and different values of the coupling parameter. There is a dramatic manifestation of the transition between the two types of dynamics that define parametric regions of regular and irregular behaviour. The Lyapunov exponent, phase portraits, Poincaré sections and power spectra are calculated. The computer simulations show that the vibrational anharmonicity favours the regular behaviour of the system.