2021A&A...649L...4A

We report the detection of the oxygen-bearing complex organic molecules propenal (C₂H₃CHO), vinyl alcohol (C₂H₃OH), methyl formate (HCOOCH₃), and dimethyl ether (CH₃OCH₃) toward the cyanopolyyne peak of the starless core TMC-1. These molecules were detected through several emission lines in a deep Q-band line survey of TMC-1 carried out with the Yebes 40m telescope. These observations reveal that the cyanopolyyne peak of TMC-1, which is a prototype of a cold dark cloud rich in carbon chains, also contains O-bearing complex organic molecules such as HCOOCH₃ and CH₃OCH₃, which have previously been seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C₂H₃OH in space and the first time that C₂H₃CHO and C₂H₃OH have been detected in a cold environment, adding new pieces to the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2±0.3)x10¹¹cm^–2, (2.5±0.5)x10¹²cm^–2, (1.1±0.2)x10¹²cm^–2, and (2.5±0.7)x10¹²cm^–2 for C₂H₃CHO, C₂H₃OH, HCOOCH₃, and CH₃OCH₃, respectively. Interestingly, C₂H₃OH has an abundance similar to that of its well-known isomer acetaldehyde (CH₃CHO), with C₂H₃OH/CH₃CHO∼1 at the cyanopolyyne peak. We discuss potential formation routes to these molecules and recognize that further experimental, theoretical, and astronomical studies are needed to elucidate the true formation mechanism of these O-bearing complex organic molecules in cold interstellar sources.