Intramolecular vibrational relaxation and spectra of CH and CD overtones in benzene and perdeuterobenzene

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Abstract
A theoretical model is presented for the vibrational dynamics of highly excited CH and CD overtones in benzene and perdeuterobenzene. The origin, path, and time scale for the overtone relaxation are described. The critical near resonant interaction responsible for the energy flow from an excited CH(D) oscillator to the ring is a Fermi resonance coupling, identified by Sibert, Reinhardt, and Hynes [Chem. Phys. Lett. 92, 455 (1982)]. Quantum overtone spectra are calculated both from time independent and time dependent perspectives and good qualitative agreement is found with the experimental overtone spectra of Reddy, Heller, and Berry [J. Chem. Phys. 76, 2814 (1982)]. Some expected consequences for future experiments on benzene and related systems are indicated.