239th ACS National Meeting & Exposition
"Recent Advances in Observational and Experimental Astrochemistry"
Session of the Division of Physical Chemistry
March 21-25, 2010
San Francisco, California
Titles and Abstracts for CCU Participants
|Sunday, March 21, 2010|
“Testing the limits of complex organic chemistry in the interstellar medium”
Susanna Widicus Weaver, Emory University
Abstract: Fundamental biological molecules such as amino acids and sugars have been discovered in meteorites, but none of these species have yet been definitively detected in the interstellar medium (ISM). While both the number of detected interstellar molecules and their chemical complexity continue to increase, understanding of the processes leading to their formation is lacking. Recent chemical models suggest that organic radicals formed during the photolysis of interstellar ices provide the building blocks for the larger organic molecules found in star-forming regions. In order to investigate these interstellar prebiotic chemical pathways, we are developing a terahertz (THz) cavity ringdown spectrometer to study the unstable, reactive molecules that are key reaction intermediates. In this talk, I will present the initial results of the instrument development and spectroscopic studies. I will also outline our future plans for this instrument and the link to our ongoing projects in observational astronomy and astrochemical modeling.
“Broadband Fourier transform microwave spectroscopy for laboratory identification of molecules of interest in interstellar chemistry”
Brooks H. Pate, University of Virginia
Abstract: Recent advances in high-speed digital electronics have made it possible to design Fourier transform microwave (FTMW) spectrometers with high instantaneous bandwidth. These spectrometers use chirped pulse excitation to polarize molecules over bandwidths exceeding 10 GHz. The subsequent broadband free induction decay is digitized using a high-speed digital oscilloscope with 50 Gs/s digitization rates. Spectrometer design principles to enhance the sensitivity for low-abundance molecules, to increase the data throughput for deep averaging, and to extend operation to higher frequency will be described. Applications of chirped-pulse FTMW spectrometers to the identification of high energy isomers and molecular ions produced in electric discharge pulsed-jet sources will be highlighted. The characterization of the less stable conformer of methyl formate will be presented along with evidence for its presence in SgrB2(N) from the PRIMOS survey using the NRAO Green Bank Telescope.
“Molecular cations and anions in the laboratory and in space ”
Michael C. McCarthy, Harvard-Smithsonian Center for Astrophysics
Abstract: The application of Fourier transform microwave spectroscopy to
supersonic molecular beams has developed into a remarkably sensitive
technique for studying unstable molecules. It has proven particularly
effective for the detection of the kind of large reactive carbon chains
often found in space, such as polyynes, radicals, and carbenes, whose
rotational spectra are greatly simplified at the very low rotational
temperature that is readily achieved in a supersonic molecular beam
source. Although laboratory detection remains challenging, more than
150 new carbon chains, carbon rings, and small atomic clusters
containing silicon and sulfur have been detected and spectroscopically
characterized in our laboratory. Some of the most recent laboratory
discoveries include protonated molecules such as HSCO+, HSCS+, and HSO2+. On the basis of the laboratory data, more than 10% have been detected in space, including negatively charged ions (anions), a long-postulated but never before observed class of interstellar molecules. This talk will provide a broad overview of our recent work, illustrating with a few specific examples the power of our laboratory techniques, and how these techniques can be applied to challenging problems relevant to combustion and interstellar chemistry.
|Wednesday, March 24, 2010|
“Current status of chemical models of interstellar sources ”
Eric J. Herbst , The Ohio State University
Abstract: Networks of chemical reactions are used in simulations of the chemistry of different sources in the interstellar medium. These simulations have been undertaken since the early 1970's when the networks consisted of small numbers of gas-phase reactions. Current networks have grown to more than 5000 gas-phase reactions and a large number of surface reactions that occur on interstellar grains. Although the gas-phase chemical processes can be treated with standard rate equations, the surface chemistry represents a more complex problem given the small size of interstellar grains. It seems important at this stage to consider how useful and accurate current large chemical models are, especially those used to study portions of the interstellar medium that are collapsing to form new generations of stars and planetary systems.
Division of Physical Chemistry: Poster Session
“Methanol photodissociation and its effects on complex chemistry in the interstellar medium ”
Jacob C. Laas, Susanna L. Widicus Weaver, Robin T. Garrod
Abstract: A variety of complex organic molecules have been detected in the interstellar medium, but the chemical pathways to these molecules are not well-understood. Grain surface chemistry plays a fundamental role in their formation, and radical-radical combination reactions on ice surfaces form these molecules during star formation. These radicals form from photolysis of interstellar ice constituents, including water, methanol, ammonia, and formaldehyde. Methanol photodissociation is a major source of radicals that ultimately react to form complex organics. However, the branching ratios for this process are not well-characterized. To this end, we are conducting laboratory measurements of methanol photodissociation via quantitative terahertz (THz) spectroscopy. We are also using chemical modeling to test the effects of these branching ratios on the formation of complex organics in interstellar environments. Here we present the initial results of the laboratory and modeling work and discuss the implications of these results for interstellar complex organic chemistry.