Search

Solar-type protostars harbor highly deuterated complex organics. While this degree of deuteration may provide important clues in studying the formation of these species, spectroscopic information on multiply deuterated isotopologs is often insufficient. In particular, searches for triply deuterated methanol, CD$_3$OH, are hampered by the lack of intensity information from a spectroscopic model. The aim of the present study is to develop such a model of CD$_3$OH in low-lying torsional states that is sufficiently accurate to facilitate further searches for CD$_3$OH in space. We performed a new measurement campaign for CD$_3$OH involving three spectroscopic laboratories that covers the 34 GHz-1.1 THz and the 20-900 cm$^{-1}$ ranges. The analysis was performed using the torsion-rotation Hamiltonian model based on the rho-axis method. We determined a model that describes the ground and first excited torsional states of CD$_3$OH, up to quantum numbers $J \leqslant 55$ and $K_a \leqslant 23$, and we derived a line list for radio-astronomical observations. This list is accurate up to at least 1.1 THz and should be sufficient for all types of radio-astronomical searches for this methanol isotopolog. It was used to search for CD$_3$OH in data from the Protostellar Interferometric Line Survey of IRAS 16293-2422 using ALMA. CD$_3$OH is securely detected in the data, with a large number of clearly separated and well-reproduced lines. We detected lines belonging to the ground and the first excited torsional states. The derived abundance of CD$_3$OH relative to non-deuterated isotopolog confirm the significant enhancement of this multiply deuterated variant. This finding is in line with other observations of multiply deuterated complex organic molecules and may serve as an important constraint on their formation models., Comment: Astronomy and Astrophysics, in press. 21 pages, including figures, tables, and appendices; abstract shortened

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)

International audience; We present a new study of the millimeter and submillimeter wave spectra of the thioacetaldehyde molecule, CH3CHS, a sulfur-bearing analog of the ubiquitous interstellar molecule acetaldehyde (CH3CHO). Here, we present a laboratory investigation aimed at determining accurate spectroscopic parameters for CH3CHS to enable astronomical searches for this molecule using radio telescopes at millimeter and submillimeter wavelengths. New laboratory measurements have been carried out between 150 and 660 GHz using the spectrometer of PhLAM in Lille (France). Rotational transitions up to J = 60 were assigned in the ground, first, and second excited torsional states of thioacetaldehyde and fit using the RAM Hamiltonian model. The final fit includes 62 parameters to give an overall weighted root-mean-square deviation of 0.9. On the basis of our spectroscopic results, CH3CHS was searched for, but not detected, in data from the Atacama Large Millimeter/submillimeter Array (ALMA) between 84 GHz and 114 GHz toward the hot molecular core Sgr B2(N2). The non-detection implies that thioacetaldehyde is at least 90 times less abundant than acetaldehyde in this source. We also searched for but found no evidence of thioacetaldehyde in a number of prestellar and protostellar sources targeted by the Astrochemical Surveys at IRAM (ASAI) Large Program in nearby low-mass star forming regions.

We present a new global study of the millimeter (mm) wave, submillimeter (sub-mm) wave, and terahertz (THz) spectra of the lowest three torsional states of methyl mercaptan (CH$_3$SH). New measurements have been carried out between 50 and 510 GHz using the Kharkiv mm wave and the Cologne sub-mm wave spectrometers whereas THz spectra records were used from our previous study. The new data, involving torsion-rotation transitions with $J$ up to 61 and $K_a$ up to 18, were combined with previously published measurements and fit using the rho-axis-method torsion-rotation Hamiltonian. The final fit used 124 parameters to give an overall weighted root-mean-square deviation of 0.72 for the dataset consisting of 6965 microwave (MW) and 16345 far-infrared line frequencies sampling transitions within and between the ground, first, and second excited torsional states. This investigation presents a two-fold expansion in the $J$ quantum numbers and a significant improvement in the fit quality, especially for the MW part of the data, thus allowing us to provide more reliable predictions to support astronomical observations., Comment: 12 pages; Astron. Astrophys., in press

We present a new global study of the millimeter, submillimeter and far-infrared (FIR) spectra involving the three lowest torsional states of acetone ((CH3)2CO). New microwave measurements have been carried out between 34 and 940 GHz using spectrometers in IRA NASU (Ukraine), and PhLAM Lille (France). The FIR spectrum of acetone has been recorded on the AILES beamline of the SOLEIL synchrotron facility. The new data involving torsion–rotation transitions with J up to 90 and Ka up to 52 were combined with previously published measurements and analyzed using a model developed recently to study the high resolution spectra of molecules with two equivalent methyl rotors and C2v symmetry at equilibrium (PAM_C2v_2tops program). The final fit included 117 parameters to give an overall weighted root-mean-square deviation of 0.85 for the dataset consisting of 29,584 microwave and 1116 FIR line frequencies belonging, respectively, to the three lowest torsional states (ν12,ν17) = (0,0), (1,0), (0,1) and to the observed fundamental band associated with the methyl-top torsion mode (ν12,ν17) = (0,1) ← (0,0). The high values of rotational quantum numbers involved in this study provide an opportunity to test the performance of the PAM_C2v_2tops program approach for the case of highly excited rotational states.