Tropolone monomer: Vibrational spectrum and proton tunneling

Infrared matrix-isolation spectra are reported for the tropolone monomers C₇H₅O₂H and C₇H₅O₂D. Tropolone possesses an intramolecular hydrogen bond and the possibility for proton tunneling from one oxygen atom to the other. Clearcut multiplets attributed to tunneling are observed for the OD stretching mode and for heavy atom modes of both C₇H₅O₂D and C₇H₅O₂H. The (mixed) carbonyl stretching mode particularly seems to facilitate tunneling from one conformation to the other. The tunneling phenomena suggests that tropolone monomer has nearly C_2v symmetry. As a crude estimate, the tunneling potential energy barrier is calculated to be less than 5600 cm^?1 in the ground electronic state of C₇H₅O₂D. The barrier is lower in the $\text{Π}{}^1$ electronic state than in the ground electronic state. A vibrational assignment that encompasses most of the 39 fundamental modes is proposed. The vibrations are classified using C_2v symmetry species and a parallel vibrational analysis is presented for tropone, C₇H₆O, which is a true C_2v molecule.