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New Pathways for the Formation of Complex Organics and Prebiotic Synthesis in the Gas Phase, in Nanoclusters, and on Dust Grain Surfaces

Wednesday, April 1, 2009 - 4:00pm

National Radio Astronomy Observatory, Charlottesville


M. Samy El-Shall

Professor of Chemistry

Affiliate Professor of Chemical Engineering

Virginia Commonwealth University, Richmond, VA 23284-2006

Tel: (804) 828-3518; Fax: (804) 828-1280


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Many complex organics including polycyclic aromatic hydrocarbons and species with 30-or-more carbon atoms are present in flames and combustion processes as well as in interstellar clouds and solar nebulae. Prebiotic synthesis in interstellar clouds and solar nebulae contributes complex organics for the origins of life. Gas phase reactions and gas-grain interactions involving interstellar molecules and dust particles lead to a variety of complex organic molecules including abundant precursor molecules for life such as H 2CO, HCN and NH 3. Our research addresses two major questions: (1) how are simple organic compounds assembled into more complex molecular systems? And (2) what are the essential processes and pathways by which complex systems can develop those basic properties that are critical to life’s origins?

Recently, we reported the first conclusive evidence for the efficient formation of benzene ions within gas phase ionized acetylene clusters. Acetylene, the smallest organic molecule that can be polymerized, and benzene, the smallest cyclic aromatic molecule, are both present in interstellar space. In this talk, we present evidence from laboratory experiments for the formation of complex organics by gas phase and intracluster reactions of the benzene, phenylium, pyridine, phenylacetylene and benzonitrile cations with acetylene molecules. Synthetic channels with increased numbers of carbon atoms are found in all the observed reactions. The observed chemistry under a wide range of experimental conditions, including extreme temperatures as high as 650 K and as low as 120 K, strongly implies a series of ion-molecule reactions that can lead from a simple molecule such as acetylene to polycyclic organics incorporating nitrogen.

As to reactions on grain surfaces, the generation of nanoparticles from the Allende CV3 and Murchison CM2 meteorites using the Laser Vaporization-Controlled Condensation method will be presented. The highly porous aggregated nanoparticles are remarkably similar to Interstellar Dust Particles (IDPs). The results will be discussed in terms of the mechanisms of formation of complex organic molecules and the models of early environments in which organic chemical synthesis could occur.




M. Samy El-Shall is a Professor of Chemistry and Chemical Engineering at Virginia Commonwealth University (VCU). He received his B.S. and M.S. degrees from Cairo University in Egypt, and a Ph.D. in Physical Chemistry with Distinction from Georgetown University in 1986. He did postdoctoral research in nucleation and clusters at the University of California, Los Angeles from 1986-1989. His research interests are in the general areas of molecular clusters, homogeneous, binary and ion-induced nucleation, gas phase and cluster polymerization, synthesis and properties of nanostructured materials, photoluminescence properties of nanoparticles and nanocatalysis. He has published over 180 papers in the most prestigious and widely read journals of Chemistry, Chemical Physics and Nanomaterials. Dr. El-Shall was awarded several US patents (7 issued, 4 pending) on the synthesis of nanoparticles, photoluminescence of silicon nanocrystals, magnetic intermetallic nanoparticles, nanoparticle catalysts, and nanoparticle additives for fuels and lubricants. Dr. El-Shall received the Exxon Education Award in 1994 and 1995. He was the recipient of the Distinguished Scholar Award of the College of Humanities and Sciences at VCU in 1996. He has been selected as a VCU Board of Visitors Teaching Fellow in 1998. In 1999, he was honored with the Outstanding Faculty Award of the State Council of Higher Education of Virginia (SCHEV), Virginia's highest faculty honor. Dr. El-Shall has been a member of the Editorial Advisory Boards of the Journal of Physical Chemistry (2005-2008), the Journal of Photoenergy and the Physical Chemistry Reviews. He was the chairman of the “International Conference on Nanoparticles from the Vapor Phase Synthesis with Chemical and Biochemical Applications” in Davos, Switzerland, 2004. He also organized and chaired three US-Egypt workshops, sponsored by the National Science Foundation, on Advanced Materials (2000), Lasers in Chemistry and Biomedical Applications (2004) and Nanomaterials and Nanotechnology (2005). Dr. El-Shall organized and chaired the “First US-North Africa International Workshop on Nanomaterials and Nanotechnology” that was held in Tunis in March 2007. He was also the chairman of the “New Materials and Nanotechnology” conference of the 5 th Congress of Scientific Research Outlook in the Arab World that was held in Fez-Morocco, October 26-30, 2008.

Dr. El-Shall’s research has been supported by the National Science Foundation, NASA, NIST, Petroleum Research Fund, Dreyfus Foundation , Jeffress Memorial Trust, Exxon, Dow Corning, Philip Morris, and Afton Chemical.