Résumé
Abstract Room temperature millimeter‐wave rotational spectroscopy supported by high level of theory calculations have been employed to fully characterise the conformational landscape of 3‐Methoxyphenol, a semi‐volatile polar oxygenated aromatic compound precursor of secondary organic aerosols in the atmosphere arising from biomass combustion. While previous rotationally‐resolved spectroscopic studies in the microwave and in the UV domains failed to observe the complete conformational landscape, the 70–330 GHz rotational spectrum measured in this study reveals the ground state rotational signatures of the four stable conformations theoretically predicted. Moreover, rotational transitions in the lowest energy vibrationally excited states were assigned for two conformers. While the inertial defect of methoxyphenol does not significantly change between conformers and isomers, the excitation of the methoxy out‐of‐plane bending is the main contribution to the non‐planarity of the molecule.