A Computational Study of the Mechanisms for the Incorporation of a Nitrogen Atom into Polycyclic Aromatic Hydrocarbons in the Titan Haze

• Published in: Icarus (New York, N.Y. 1962) Vol. 154; no. 2; pp. 516 - 521
• Main Authors: Ricca, Alessandra, Bauschlicher, Charles W., Bakes, E.L.O.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-12-2001
• Subjects: stratospheric chemistry; Titan; aromatics
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1006/icar.2001.6694

Current photochemical models of Titan, Saturn's largest satellite, include chemical reactions producing molecules composed of up to six carbon atoms and then extrapolate straight to aerosols, such as tholins. Laboratory evidence suggests that polycyclic aromatic hydrocarbons containing nitrogen atoms are formed during simulations of Titan's atmosphere. This paper presents preliminary work on reactions that produce nitrogenated aromatic molecules containing up to 12 nonhydrogen atoms. These species would help bridge the gap between the small molecules and the aerosols in Titan's stratosphere. We have determined the barriers and reaction energies for the incorporation of nitrogen into the rings of polycyclic aromatic hydrocarbons. The presence of a nitrogen atom increases the barrier heights relative to the pure hydrocarbon species to about 15 kcal/mol. Nitrogen in the ring promotes the formation of additional hydrocarbon rings by lowering the ring closing barrier to about 4 kcal/mol. Inclusion of these species in photochemical models of Titan is indicated.