Submillimeter wave spectroscopy of propanoic acid (CH3CH2COOH) and its ISM search

8 pags., 3 figs., 3 tabs.Three compounds with a CHO formula have been detected in the Interstellar Medium (ISM): ethyl formate (CHCHOC(O)H), methyl acetate (CHOC(O)CH) and very recently hydroxyacetone (CHC(O)CHOH). The higher thermodynamic stability of another isomer, the propanoic acid (CHCHC(O)OH), clearly suggests that this molecule should be considered as a possible candidate for ISM detection. To provide reliable predictions for astronomical use in the millimeter and submillimeter wave ranges we performed a new study of propanoic acid rotational spectrum up to 545 GHz. The analysis of large amplitude methyl top torsional motion in this molecule was carried out using the rho axis method and the RAM36 program code. More than 3200 lines corresponding to the rotational transitions in the ground and first excited methyl top torsional states were newly assigned and fit within experimental error. This enabled us to produce new predictions which were used to search for propanoic acid in two high-mass star-forming regions: SgrB2 (public IRAM 30 m) and Orion KL (ALMA Science Verification). We report a non-detection of propanoic acid in these clouds and derive upper limits to the column density.LM/RAM/JCG acknowledge the support of the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU. JCG thanks also the Centre National d’Etudes Spatiales (CNES) for a grant. BT and JC thank Ministerio de Ciencia e Innovaci ́on of Spain (MICIU) for funding support through projects AYA2016-75066-C2-1-P, PID2019-106110 GB-I00, PID2019-107115 GB-C21/ AEI/ 10.13039/ 501100011033, and PID2019-106235 GB-I00. We also thank ERC for funding through grant ERC2013-Syg-610256-NANOCOSMOS. This paper makes use of the following ALMA data: ADS/JAO. ALMA⧹♯2011.0.00009.SV. ALMA is a partnership of ESO (representing its member states), NSF (USA), and NINS (Japan) with NRC (Canada), NSC, and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. This work was also based on observations carried out with the IRAM 30-meter telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain