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The present paper describes recent results on the classical and quantum description of modes in anharmonically coupled oscillators in isolated molecules. In the low energy regime, the vibrational motion is quasiperiodic and can be regarded as being in regular ""Anharmonic Modes"". In the high energy regime, the motion appears ‘stochastic’ (but deterministic). We examine this behavior for OCS and other model systems using classical trajectories to calculate the molecular $spectrus1$ in both regimes. The effects of resonance interaction on molecular vibration of a model system are also examined using this technique. The correlation of these results with a recent exact quantum calculations on simple systems is made. The quantum mechanical wave function also shows two types of $behaviour2$ which correspond to the quasiperiodic and stochastic types of classical behavior. We have attributed the latter behavior to the system’s having many avoided crossings in the $eigenvalues.33$