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

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.

Intramolecular dynamics. I. Curvilinear normal modes, local modes, molecular anharmonic Hamiltonian, and application to benzene

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Vibrational overtone spectroscopy of pyridine and related compounds

“…However the explanation for the location and shape of the absorption bands is still incomplete. Theoretical work 3 modeled the widths of these overtone absorptions using intramolecular vibrational relaxation pathways. Experimental work 4 on the second overtone spectrum of jet cooled benzene indicates homogeneous linewidths as small as 4 cm-I.…”

Theoretical Overview of Chemical Dynamics

“…E.g., if a laser excites motion that is predominantly CH stretch motion in benzene, how quickly does this energy move into other degrees of freedom in the molecule, and which of the other degrees of freedom are most effective in accepting this energy? 32 This question becomes even more interesting if some degrees of freedom lead to bond-breaking, in which case one is talking about unimolecular reactions. 10 The rigorous quantum mechanical description of unimolecular reactions is that of Siegert eigenstates.…”