Observation of Rotational Isomers I:  A ZEKE and Hole-Burning Spectroscopy Study of 3-Methoxyphenol

Three rotational isomers of 3-methoxyphenol have been studied using two-color resonance-enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. Hole-burning spectroscopy was employed to confirm the presence of three isomers in the REMPI spectrum (S1 band origins were identified at 35 974, 36 034 and 36 202 ± 1 cm-1 for isomers I, IV, and III, respectively). ZEKE spectra recorded via the S1 states of the isomers provide adiabatic ionization energies of 65 228, 64 741, and 65 648 ± 5 cm-1, respectively. The isomers are assigned with the aid of HF/cc-pVDZ, MP2/cc-pVDZ, and B3LYP/cc-pVDZ ab initio and density functional theory calculations. We discuss the characteristics of the 3-methoxyphenol rotational isomers by comparing the REMPI and ZEKE spectra with those of other substituted benzenes.