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.H2O intermolecular hydrogen bond by the -OCH3 group.