2025ApJ...981...64I

Laboratory experiments on interstellar ice analogs have demonstrated that ice mixtures containing acetaldehyde (CH₃CHO) and hydrogen cyanide (HCN) in the presence of ammonia (NH₃), water (H₂O), or an NH₃/H₂O mixture allow the formation of the chiral molecule lactonitrile (2-hydroxypropionitrile; CH₃CH(OH)CN). These findings place lactonitrile among possible interstellar molecules, especially when its methyl-shortened derivative glycolonitrile and the precursors are known interstellar species. To support the search for lactonitrile in interstellar space, we present measurements under supersonic expansion conditions in the 6-16 GHz frequency range, along with a detailed analysis of its room-temperature rotational spectrum from 75 to 325 GHz. Improved and extended sets of molecular parameters, determined from the newly measured data and selected literature measurements, are obtained for two conformers of lactonitrile, with accuracies conducive to reliable interstellar searches. We report the nondetection of lactonitrile toward the main hot core Sgr B2(N1S), with a column density upper limit 1 order of magnitude higher than the upper limit derived for the related molecule glycolonitrile.