Structure and vibrations of catechol(methanol)1 in the S and S1 state

Abstract

The structure as well as the inter- and intramolecular vibrations of the catechol (methanol)1 cluster are investigated both experimentally and theoretically. By using resonant two-photon ionization (R2PI) and dispersed fluorescence (DF) spectroscopy, the vibrational transitions of the S0 and S1 state are obtained. In order to find the corresponding vibrations of the S0 and S1 state, DF spectra are recorded by pumping the electronic origin and the most intense vibrations of the R2PI spectrum. According to ab initio calculations performed at the Hartree–Fock level [6-31G(d,p) basis], including MP2, BSSE, and ZPE (zero point energy) corrections, the most stable structure turns out to be translinear. The calculated vibrational frequencies are in close agreement to the experimental values. Since the catechol(methanol)1 cluster has no symmetry, all intermolecular fundamental vibrations of the S0 and S1 state spectra can be assigned. A large number of combination bands and overtone vibrations are observed in the low frequency region (<200 cm−1) of the S0 and S1 state spectra. From the DF spectrum obtained by pumping the low frequency ρ1 vibration, it can be concluded that the catechol(methanol)1 cluster undergoes a geometry change in the S1 state. The OH…O bond turns out to be nonplanar with respect to the aromatic plane. This confirms the results reported for catechol and the catechol(H2O)1 cluster.