Carbon Chain Formation under Simulated Circumstellar Conditions

Carbon-chain molecules serve as precursors for complex molecules in the interstellar medium and act as indicators of both current physical conditions and chemical evolutionary trends. They hold significant importance in interstellar chemistry. Although typical carbon-chain molecules like polyynes (C₄H₂, C₆H₂) and cumulenic chains (C₃H₂ up to C₆H₂) have been observed in the IRC+10216 star and CRL618 nebula, the formation mechanism of carbon chains in the circumstellar envelopes (CSEs), and in particular the role of the radicals ^•C_nH (^•C₂H up to ^•C₈H) in the growth of chemical complexity, remains under investigation. The development of an ultrahigh temperature pyrolysis photoionization/electron ionization time-of-flight mass spectrometer (UT-Py-PI/EI-TOFMS) in our laboratory astrophysics simulation experiments provides insights into the formation process of these interstellar molecules. Detection of a range of long-chain polyyne molecules in this apparatus indicates that rapid radical reactions of ^•C_2nH with unsaturated hydrocarbons govern the growth process of long-chain polyynes. These findings offer evidence for the formation of carbon-chain molecules in the envelopes of the AGB star and simulated their formation in the laboratory. Furthermore, this laboratory simulation successfully reproduces other interstellar molecules such as fullerenes.