Intramolecular vibrational energy flow in model four-atom systems

Intramolecular energy transfer from local bond modes is studied by using quasiclassical trajectories. The energy in a local mode as a function of time is computed to determine the nature and time scale for the decay of local mode excitation. Variations of four basic models are examined: HCCC, HOOH, HNNH, and HC≡CH. Potential-energy surfaces for the models are sums of Morse functions for bond stretches and harmonic bending functions. The potential for HOOH torsional motion is represented by a truncated Fourier cosine series. The emphasis of the study is on H₂O₂. The decay of OH overtone excitation is characterized by slow, irreversible flow of energy out of the OH as a function of time. The rate of energy transfer is strongly dependent upon the OOH bending and the torsional motions.