QUASI-ACTION VARIABLE FOR CHAOS IN CHEMICAL-DYNAMICS

Is proposed quasi-action variable as a means to analyze the onset of c lassical chaos in molecular vibrational systems. The basic idea rests on a symplectic area generated by a classical trajectory in phase spac e, from which the geometrical information of a torus and its breakdown in extracted. The Fourier spectrum of the time derivative of this sym plectic area centers on the following definition and findings: (1) in an integrable system, the action variables can be simply calculated in terms of the above Fourier amplitudes, (2) the quasi-action variable is also defined in a similar way and is a good approximation to the co rresponding action variable, but (3) the construction of the quasi-act ion variable does not depend on the integrability and hence it it defi ned as well even for a chaotic system, and (4) the characteristics of chaos can be analyzed in the continuous spectrum of the quasi-action v ariable. Some numerical examples of the quasi-action variable are pres ented for a system of what we call phase-space large amplitude motion. As a byproduct, a simple method has been devised to calculate very ac curate frequencies and amplitudes from the so-called Fast-Fourier-Tran sform (FFT) spectra without resorting to the so-called window techniqu e.