Internal Rotation and Intermolecular Vibrations of the Phenol−Methanol Cluster: A Comparison of Spectroscopic Results and Ab Initio Theory

The vibronic spectra of five deuterated species of the binary phenol−methanol cluster are compared to the intermolecular vibrational frequencies of an ab initio-based normal-mode analysis. Isotopomers with equal mass could be distinguished experimentally using spectral hole-burning spectroscopy. The vibronic bands of phenol−methanol are split into A and E components because of the internal rotation of the methyl group. This torsional splitting is increased for three of the intermolecular vibrations because of coupling to the large-amplitude motion. Guided by comparison to an ab initio normal-mode analysis and by the torsional splitting of some of the vibronic bands, a complete intermolecular vibrational assignment for the phenol−methanol cluster is presented.