The structure of the binary phenol-methanol cluster:: A comparison of experiment and ab initio theory

The structure, energetics, vibrations and barrier to internal rotation of the binary phenol-methanol cluster are calculated at different levels of theory and compared to the results of a rotationally resolved S-1 <-- S-0 electronic spectrum. The structure of the phenol-methanol cluster is determined by a hydrogen bond and by a dispersive interaction of the methyl group with the aromatic ring. To account for the correct balance between these two attractive forces, computational methods have been employed which include electron correlation. The barrier to internal rotation of the methyl group has been determined from the experiment and compared to the lowest energy path at a relaxed ab initio energy surface. Furthermore, an ab initio normal mode analysis is performed and compared to experimental intermolecular vibrational frequencies for both electronic states. (C) 2001 Elsevier Science B.V. All rights reserved.