We report here the chemical reaction mechanisms by which complex organic molecules including large polycyclic aromatic hydrocarbons, known to be common in the atmosphere of Titan, and may be in other exoplanetary atmospheres, are formed. Organic molecules are found in diverse astrophysical environments as well. Molecular ions, both positive and negative ions, are present in Titan’s upper atmosphere. Barrierless ion-molecule interactions may play a major role in guiding ions and molecules towards each other and initiating growth in these atmospheres. We study neutral as well as ion-neutral association pathways to determine whether they are a viable means for synthesizing nitrogen containing hydrocarbon chains and cyclic molecules, by employing a variety of quantum chemical methods, such as coupled cluster and density functional theory methods. Where possible, the results from our calculations are compared with the results from experimental studies such as plasma discharge and ion-mobility experiments. We have investigated the process of growth, structural features, nature of bonding, reaction mechanisms, reaction kinetics, and spectroscopic properties of the ensuing products after pairing carbon, hydrogen, and nitrogen-containing precursors. Ab-initio molecular dynamics trajectory studies of the ion-neutral association pathways involving pure-carbon and nitrogen-containing precursors at various temperatures reveal interesting details about the cyclic molecule (such as pyridine) formation process. We found that hydrocarbon reactants with suitable starting geometries and specific stoichiometric compositions prefer cyclic molecule formation rather than chains. Some of the association products we investigated have large oscillator strengths for charge-transfer type electronic excitations in the near infrared and visible regions of the electromagnetic spectrum.

Dynamics of pure and N-substituted cyclic aromatic hydrocarbon formation in the gas phase

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.