Determination of the structures and barriers to hindered internal rotationof the phenol-methanol cluster in the S-0 and S-1 states

The rotationally resolved S-1 <-- S-0 electronic spectrum of the hydrogen-b onded phenol-methanol cluster has been analyzed. Due to the internal rotati on of the methyl group in the methanol moiety, the spectrum of the electron ic origin of phenol-methanol is split into A and E subtorsional bands. From a perturbation analysis of the torsional-rotational structure of the elect ronic origin, the threefold barriers to internal rotation of the methyl gro up could be determined to be 170 cm(-1) in the S-0 state and 150 cm(-1) in the S-1 state. The perturbation analysis yielded the angle between the inte rnal rotor axis and the inertial axes of the cluster, which allows the dete rmination of the geometry of the hydrogen bond in both electronic states. ( C) 2000 Published by Elsevier Science B.V. All rights reserved.