Rotational isomers of 1-methoxynaphthalene: A combined study by ultraviolet laser spectroscopy in a supersonic jet and ab initio theoretical calculation

Two rotational isomers of 1-methoxynaphthalene have been identified in the collision-free environment of a supersonic jet expansion by the use of laser-induced fluorescence spectroscopy and photoionization time-of-flight mass spectrometry. In the fluorescence excitation spectra, the features corresponding to the higher-energy conformer are sensitive to conditions of the nozzle expansion, and this has been attributed to a shallow energy minimum of the conformer on the methoxy torsional potential surface. The observations are consistent with the ab initio (HF, MP2//HF, and DFT/B3LYP) theoretical results that in addition to the most stable trans planar conformation, the molecule has a second higher-energy conformer (∼9 kJ/mol) in which the methoxy group is perpendicular to the plane of the naphthalene ring.