===== On Propadienone in the Interstellar Medium ===== G. Esplugues, J. C. Loison, M. Agúndez, G. Molpeceres, N. Marcelino, B. Tercero, and J. Cernicharo\\ reported on the\\ **[[https://doi.org/10.1051/0004-6361/202557355|Discovery of Linear Propadienone — Study of the Cof linear and Cyclic H2C3O and H2C3S in TMC-1]]**\\ //Astron. Astrophys.// **705**, Art. No. A206 (2026).\\ The elusive propadienone was detected in two //a//-type transitions with //Ka// = 0 and //J// = 4 − 3 and 5 − 4 near 34.6 and 43.2 GHz in the course of a molecular line survey in the 31.0 to 50.3 GHz region carried out with the 40 m Yebes telescope. The very small tunneling splitting of ~45 kHz was not resolved. The identification of two transitions can be considered as quite secure in TMC-1. Assuming a rotational temperature of 4.8 K, taken from the isomeric //ortho//-cyclopropenone, a cyclopropenone to propadienone ratio of about 9 was derived, while the propynal to propadienone ratio is roughly 23.\\ \\ ---- Contributor(s): H. S. P. Müller; 02, 2026 ----