Pseudocarbynes: Progenitors for Complex Organic Molecules in the Outer Solar System

Primitive meteorites contain carbonaceous materials that range from kerogen-like macromolecules to organic molecules such as amino acids and polyols. In addition to their origins in the circumstellar envelopes of carbon-rich stars, many complex organic molecules have been conjectured to form in the interstellar medium (ISM), either in free space or on grain surfaces. However, little is known about the mechanisms responsible for their formation. Also, there have been several reports over the last decades regarding the stability of linear acetylenic carbon chains (polyynes) in the condensed phase. We recently showed (Tarakeshwar et al. JPCL, 2016) that such chains can be stabilized by metal clusters, forming polyyne complexes that we call pseudocarbynes. Such pseudocarbynes may have been overlooked in the ISM because their vibrational spectra are, within experimental uncertainties, identical to metal-free species. Moreover, their predicted remarkable catalytic and magnetic properties suggest that they facilitate the formation of complex, multi-atom, organic molecules. Based on high-level ab initio calculations, we present results on the pathways leading to the formation under ISM and Outer Solar System conditions of some complex organic molecules from pseudocarbynes. Additionally, the results provide new insight into the gap in composition and complexity between linear molecules in the ISM, all of which contain nine or fewer C atoms, and complex molecules such as polyaromatic hydrocarbons and fullerenes.