The ALMA-PILS survey: first detection of the unsaturated 3-carbon molecules Propenal (C₂H₃CHO) and Propylene (C₃H₆) towards IRAS 16293–2422 B

Complex organic molecules with three carbon atoms are found in the earliest stages of star formation. In particular, propenal (C$_2$H$_3$CHO) is a species interest due to its implication formation more complex and even biotic molecules. This study aims search for presence C$_2$H$_3$CHO other three-carbon such as propylene (C$_3$H$_6$) hot corino region low-mass protostellar binary IRAS 16293--2422 understand their pathways. We use ALMA observations Band 6 7 from various surveys C$_3$H$_6$ towards protostar B (IRAS 16293B). report detection both 16293B, however, no unblended lines were component system, 16293A. derive column density upper limits C$_3$H$_8$, HCCCHO, n-C$_3$H$_7$OH, i-C$_3$H$_7$OH, C$_3$O, cis-HC(O)CHO 16293B. then three-phase chemical model simulate these typical prestellar environment followed by hydrodynamical collapse until birth central protostar. Different paths, successive hydrogenation radical-radical additions on grain surfaces, tested compared observational results. The simulations reproduce abundances within one order magnitude those observed best agreement rate $10^{-12}$ cm$^3$ s$^{-1}$ gas-phase reaction C$_3$ + O $\rightarrow$ C$_2$ CO. Successive hydrogenations C$_3$, HC(O)CHO, CH$_3$OCHO surfaces major crucial route organics molecules, whereas pathways addition reactions contribute C$_2$H$_5$CHO.