Classical mechanics of intramolecular vibrational energy flow in benzene. IV. Models with reduced dimensionality

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Abstract
The classical mechanics of intramolecular relaxation of benzene CH(D) local mode overtone states is studied with the molecular models HC3, DC3, and H3C3. These reduced dimensionality models provide one means to correct for the improper classical mechanical treatment of zero‐point motion in complete benzene models. They give significantly smaller homogeneous linewidths for the low energy CH(D) overtones than found from previous classical trajectory calculations for C6H6/C6D6 models. The n=3 and 5 linewidths for the DC3 model are less than 1 cm−1, while for the HC3 and H3C3 models these linewidths are approximately 5–10 cm−1. The energy transfer pathways for the deuterated and nondeuterated models are substantially different. A gradation of couplings are observed from the trajectories. For the low energy HC3/H3C3 overtones a CCH bend is initially the mode most strongly coupled to the excited CH bond, while for the higher overtones it is the B1 CC stretch. In the relaxation of the H3C3 overtones, five modes are essentially inactive on a 0.75 ps time scale.