PHYS 590 |
| The chemistry of acetylene is important in interstellar clouds as its polymerization reactions in the gas phase and on icy dust surfaces results in the formation of larger hydrocarbons and other complex molecular species. We recently reported the formation of the benzene ion from ionized acetylene clusters (Momoh, P. O.; El-Shall, M. S. J. Am. Chem. Soc. 2006, 128, 12408). The polymerization of acetylene to benzene may prove to be the first step in the formation of polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic nitrogen hydrocarbons (PANHs) which are known to be pervasive in space. Nitrogen-containing aromatics are of interest because biologically significant molecules such as DNA, RNA, and certain proteins contain nitrogen-substituted rings and an understanding of their formation mechanisms in space may aid in understanding the origin of life. Here we provide structural, thermochemical, kinetic, and dissociation results of the gas phase reactions of the pyridine radical ion, C5H5N•+, with acetylene. The primary products observed were the C5H5N∙(C2H2)n•+, C5H4N∙(C2H2)n+ (where n = 1-5), and C5H5N∙C2H2∙C5H5N•+ ions. In addition, the measured collision cross sections, Ω (300K), for the C5H5N∙C2H2•+, C5H5N∙(C2H2)2•+, and the remarkably stable C5H5N∙C2H2∙C5H5N•+ radical ions were 59.4 ±1.4 Å2, 70.0 ±1.7 Å2, and 85.6 ±1.5 Å2 respectively. The Ω-value for C5H5N∙C2H2+ suggests a structure in which an acetylene carbon binds, exothermically (-14.4 kcal/mol), to the pyridine nitrogen atom. A duplication of this bonding scheme on the other acetylene carbon is suspected to result in the formation of the C5H5N∙C2H2∙C5H5N•+ ion. |
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Sci-Mix
8:00 PM-10:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Sci-Mix
Division of Physical Chemistry |