Ab initio SCF calculations on hydrogen bonded cresol isomers

Ab initio GAUSSIAN 80 calculations with two different basis sets (STO-3G and 4–31 G*) were performed on hydrogen bonded cresol isomers for comparison with experimental data from free jet fluorescence excitation spectroscopy. Form-cresol, the calculated barriers for hindered internal rotation of the OH-group and the CH₃-group are in good agreement with experiment. The calculations show the trans-linear configuration ofp-cresol·B-clusters (B = H₂O, CH₃OH) to be more stable than the all-planar configuration. This agrees with CI calculations and microwave spectroscopic investigations of the water dimer. Calculations of both the intermolecular stretch and bend frequencies ofp-cresol·B-clusters show little dependence on the all-planar or trans-linear configuration but a strong dependence on the choice of the basis set. With the minimal basis set STO-3G, the vibrational energies are generally too high. The agreement between the calculated vibrational frequencies from the 4–31 G* basis set and the experimental values is fair.