Observation of Rotational Isomers II:  A ZEKE and Hole-Burning Spectroscopy Study of Hydrogen-Bonded 3-Methoxyphenol·Water Clusters

Three rotational isomers of 3-methoxyphenol·water have been identified using resonance-enhanced multiphoton ionization (REMPI) and hole-burning and zero electron kinetic energy (ZEKE) photoelectron spectroscopies with the aid of ab initio and density functional theory calculations. The S 1 band origins of the isomers were measured as 35 822, 35 834, and 36 019 ± 1 cm -1 and the adiabatic ionization energies as 61 049, 61 801, and 62 120 ± 5 cm -1 for isomers IV, I, and III, respectively. The frequencies of the intermolecular vibrations and the S 1 0 0 and ionization energy red shifts reveal that the water molecule hydrogen bonds more weakly to 3-methoxyphenol than to phenol. We discuss the spectral characteristics of the rotational isomers by considering the perturbation of the 3-methoxyphenol·H 2 O intermolecular hydrogen bond by the −OCH 3 group.