===== On Hydroxypropenal in Space =====

A. Coutens, J.-C. Loison, A. Boulanger, E. Caux, H. S. P. Müller, V. Wakelam, S. Manigand, and J. K. Jørgensen\\
reported on\\
**[[https://doi.org/10.1051/0004-6361/202243038|The ALMA-PILS survey: First Tentative Detection of 3-Hydroxypropenal (HOCHCHCHO) in the Interstellar Medium and Chemical Modeling of the C<sub>3</sub>H<sub>4</sub>O<sub>2</sub> Isomers]]**\\
//Astron. Astrophys.// **660** (2022), Art. No. L6.\\ 
3-Hydroxypropenal is the enol form of malonaldehyde. This enolic form is more stable than the dial because of intermolecular hydogen bonding. The molecule was identified through 11 lines in Band 7 corresponding to 19 //b//-type rotational transitions. Some of these are fully or partially blended. Two additional lines were clearly detected in Band 6 data. Rotation-tunneling transitions of //a//-type symmetry may be observable for somewhat higher excitation temperatures. However, the rest frequencies of stronger ones with low values of //K<sub>a</sub>// are so uncertain that they can not be identified unambiguously. Its fractional abundance with respect to methanol is ~10<sup>−4</sup>.\\
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H. S. P. Müller, A. Coutens, J. K. Jørgensen, L. Margulès, R. A. Motiyenko, and J.-C. Guillemin\\
published on\\
**[[https://doi.org/10.1051/0004-6361/202450029|The rotation-tunneling spectrum of 3-hydroxypropenal and confirmation of its detection toward IRAS 16293−2422 B]]**\\
//Astron. Astrophys.// **687** (2024), Art. No. A8.\\ 
The authors reported a very extensive line list from new (sub-) millimeter spectroscopic measurements. They were able to constrain the rotational temperature to 125 K. No additional lines were identified in the PILS data, but 7 additional lines were identified in archival ALMA data of the same source and with a similar spatial resolution. The column density is roughly a factor of 2.2 lower than that of propanal, a factor of about 42 lower than that of propene, and about a factor of 3 higher than that of propenal. The detection is now certainly beyond any doubt.\\
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Contributor(s): H. S. P. Müller; 04, 2022; 08, 2024

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