ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
This article addresses the importance of the structure of chaos in the phase space of planar benzene, especially around the local CH stretching mode. The structure imposes severe constraints on the ability of the classical mechanics to simulate the quantum mechanical flow of the energy out of the local mode, i.e., to simulate intramolecular vibrational relaxation (IVR). The phase space structure is inferred by computing ensemble averaged classical correlation functions and spectral densities. It is found that the region of phase space within a hyperradius of order h1/2 (which is the region corresponding to a quantum state) about the local mode is fairly well decoupled from the rest of the phase space and changes sharply from highly structured and quasiregular (although unstable) local mode character to chaotic normal mode character away from the CH bond. On one hand, the experimentally prepared quantum (packet) system must behave smoothly within the scale of h seeing only the dominant local mode character of this region. On the other hand, because some of the trajectories used to simulate the quantum flow from the local mode region are blocked and redirected back into the region, and the remainder (the majority of them) are outside the region and do not feel it, standard studies of the flow of ensembles of trajectories designed to mimic packet flow cannot be used to compute the local mode IVR rates of benzene. Instead, the scale of the phase space local mode structures, its isolated nature, and the constancy of the stability parameters everywhere in the local mode region point to the use of the stability parameters of chaotic trajectories as a measure of the IVR linewidth. These trajectories are run at the one-dimensional, local mode quantized energy, with no zero point energy in the other modes. This measure estimates the width at 10 000 cm−1 to be ∼20 cm−1, compared to the experimental width of 10 cm−1 for the local mode quantum number n=3, which is near this energy.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457922
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