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Susanna Widicus Weaver - Department of Chemistry, Emory University

Wednesday, May 27 – 11:30-12:15PM


“New THz Spectroscopic Tools for Laboratory Astrochemistry”


Several new observatories with spectral capabilities in the terahertz (THz) frequency range, including the Herschel Space Observatory (HSO), the Stratospheric Observatory for Infrared Astronomy (SOFIA), and the Atacama Large Millimeter Array (ALMA), will soon become operational. These observatories will enable broadband interstellar spectral line surveys that have sensitivity limits well below those of any preceding ground-based observations. Interpretation of these spectra, particularly the identification of new molecules, relies on supporting laboratory studies for known and suspected interstellar molecules. But THz laboratory spectral surveys have not been completed for even the most abundant interstellar molecules, let alone the majority of the nearly 150 interstellar molecules identified to date. Additionally, the sensitivity and spectral coverage offered by existing THz spectrometers have lagged behind those at shorter and longer wavelengths, limiting laboratory studies to molecules with straightforward production routes and/or strong spectral signatures.

Our group is developing new THz spectroscopic tools to enable laboratory investigation of astrophysically important molecules. Our primary goal is the development of a THz cavity ringdown spectrometer (THz-CRDS) that will rival the sensitivity of traditional infrared CRDS. This instrument will be used to study transient organic molecules that are important in interstellar prebiotic chemistry but are produced in only trace quantities in the lab. During the development phase for the THz-CRDS system, we are also using a broadband, direct absorption spectrometer in the 50 GHz – 1.2 THz frequency window to collect spectral catalogs of several highly abundant interstellar molecules. These molecules are typically known as “interstellar weeds,” as their dense, strong spectra tend to overshadow weaker interstellar lines and hamper searches for new molecules.

In this talk, I will present our progress on the THz-CRDS instrument development and the initial results from our spectral cataloging studies of interstellar weeds. I will also outline our future plans for THz laboratory spectroscopy and the links to our ongoing projects in observational astronomy and astrochemical modeling.


Related Reference(s):

“Report from the Workshop on Laboratory Spectroscopy in Support of Herschel, SOFIA, and ALMA,” Pasadena, 2006, Report Final.pdf.

R. T. Garrod, S. L. Widicus Weaver, and E. Herbst, “Complex Chemistry in Star-forming Regions: An Expanded Gas-Grain Warm-up Chemical Model," ApJ., 682, 283-302 (2008).

L. H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion–rotation global analysis of the first three torsional states ( n t = 0, 1, 2) and terahertz database for methanol," JMS, 251, 305-313 (2008).