Broadband Microwave Spectroscopy of 2’-Hydroxyacetophenone: A Complex Oxygenated Ring for Interstellar Searches

We report the laboratory rotational spectroscopy of 2’-hydroxyacetophenone, a promising candidate for the first detection of a complex oxygenated aromatic ring in the interstellar medium. The molecule is stabilized by a strong intramolecular hydrogen bond and is dominated by a single conformer with a favorable electric dipole moment (μa=0.77 D, μb=3.15 D). Spectra were recorded using chirped-pulse pulsed-jet Fourier-transform microwave spectroscopy in the 2–8 GHz region and combined with previously reported free-jet millimeter-wave absorption data. A global least-squares analysis of both data sets yields highly accurate spectroscopic constants, including the rotational constants A=2277.0739(5) MHz, B=1212.1098(3) MHz, and C=795.2762(3) MHz, while accounting for the methyl internal rotation barrier (V3=546.8(4) cm−1). These parameters were then used to generate a comprehensive set of predicted transition frequencies extending up to 163 GHz (ALMA Band 4), providing a solid foundation for future astronomical searches in cold sources.