Determination of the structures and barriers to hindered internal rotation of the phenol–methanol cluster in the S0 and S1 states Original Research Article

The rotationally resolved S1←S0 electronic spectrum of the hydrogen-bonded phenol–methanol cluster has been analyzed. Due to the internal rotation of the methyl group in the methanol moiety, the spectrum of the electronic origin of phenol–methanol is split into A and E subtorsional bands. From a perturbation analysis of the torsional–rotational structure of the electronic origin, the threefold barriers to internal rotation of the methyl group could be determined to be 170 cm−1 in the S0 state and 150 cm−1 in the S1 state. The perturbation analysis yielded the angle between the internal rotor axis and the inertial axes of the cluster, which allows the determination of the geometry of the hydrogen bond in both electronic states.