The time-dependent intramolecular vibrational dynamics of acetylene is investigated with the vibrogram method for the effective Hamiltonian obtained by Abbouti Temsamani and Herman [J. Chem. Phys. 102, 6371 (1995)]. The quantum recurrences evidenced by the vibrogram are shown to be in correspondence with emerging periodic orbits, especially, of the bending type. In this model, we find different kinds of bifurcations and, in particular, a birth of bending local modes as well as further bifurcations causing the destabilization of bending periodic orbits. This destabilization leads to a faster damping of the corresponding recurrences and to an increase in the intramolecular vibrational relaxation. A comparison with monodeuterated acetylene is also carried out.
We report on a study of intramolecular dynamics after an ultrashort excitation. We show that a semiclassical regime of the vibrational dynamics exists on an intermediate time scale between the initial dephasing on the ultrashort time of the excitation pulse and the Heisenberg time scale associated with the mean level spacing. In this semiclassical regime, intramolecular dynamics presents time recurrences at the periods of the classical orbits. The amplitudes of these semiclassical time recurrences are evaluated for classically integrable and chaotic systems using Gutzwiller and the Berry–Tabor trace formulas.
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