Dr. Susanna L. Widicus Weaver

Postdoctoral Scholar in Chemistry and Astronomy
The University of Illinois at Urbana-Champaign

Education

Current Research

My primary position at UIUC is with Ben McCall's group in the Chemistry Department, where I develop new spectroscopic and molecular sources for infrared continuous-wave cavity ringdown spectroscopy (cw-CRDS). Working with Brian Brumfield and Brett McGuire, I have developed only the third infrared cw cavity ringdown experiment to use a quantum cascade laser (QCL). We are searching for the rotationally cold, gas phase spectrum of C₆₀, the largest and most symmetric molecule ever to be studied by gas phase spectroscopy (shown on the left). We are working with a prototype 8.5 micron QCL, and have matched the world record in sensitivity for a cw-CRDS instrument. We have also constructed a high temperature oven that is combined with a supersonic source to produce rotationally cold gas phase C₆₀. We have confirmed that we are producing gas phase C₆₀, as the front flange of the vacuum chamber becomes coated with C₆₀ once the oven reaches temperatures above 600 ºC. A picture of our oven at full temperature is to the right -- it begins glowing at 450 ºC! We have benchmarked this system with the ν₈ band of CH₂Br₂. The rotational temperature obtained was 20 K and the line width was 60 MHz -- more than enough to resolve the rotational lines of C₆₀ that are separated by 180 MHz. After obtaining the CH₂Br₂ specturm, we moved on to search for C₆₀, but have had difficulties with laser mode hops at the frequency of the C₆₀ band. We have recently obtained a Faraday isolator to protect the laser from back reflections from the ringdown cavity. Once we have tested this new equipment, we will continue our search for the C₆₀ spectrum.

In addition to this project, I have also built a cw supersonic expansion discharge source out of high temperature materials to enable spectroscopic investigation of the C₆₀⁺ ion with cw-CRDS. I worked with Brian Pohrte on designing this source, and to the left is a picture of the source during operation. I then worked with several group members (too numerous to count here!) to benchmark the CRDS system with the (2,1) vibronic band of N₂⁺. Michael Wiczer developed our calibration routines, and Bogdan Negru and I analyzed the spectrum. This study has now been accepted for publication in the Journal of Molecular Spectroscopy. Please see our publications page for more information. Once we complete the C₆₀ experiment, we will move on to obtain the C₆₀⁺ spectrum.

I am also involved with the SCRIBES experiment (Sensitive, Cooled, Resolved Ion BEam Spectroscopy), which involves cw ringdown spectroscopy of a fast molecular ion beam and will use a supersonic expansion discharge source to produce very rotationally cold molecular ions. I did the initial calculations for the ion optics layout and designed the vacuum system for this experiment. Since that time, I have spent only part of my time on this experiment, while Andrew Mills has taken the lead on construction of the instrument. I have been involved in source development, though, and Andrew and I achieved a beautiful N₂⁺ ion beam a few months ago, shown on the right. After he completes construction of our difference frequency generation laser system, we plan to move on to more complicated molecular ions. Specifically, I plan to study the CH₃OH₂⁺ ion with this setup. We are collaborating with Dr. David Woon from UIUC on theoretical predictions of the rovibrational spectrum of CH₃OH₂⁺, and anticipate obtaining the spectrum of this ion within the next year.

In addition to the laboratory work, I also have a part-time appointment with the UIUC Astronomy Department. I have several ongoing observational astronomy projects. Recently, Ben and I conducted a search for the benzene derivative ortho-benzyne with the The Green Bank Telescope in collaboration with Dr. Anthony Remijan from the NRAO and Professor Robert McMahon from the University of Wisconsin-Madison. The results of this search have been published in the Astrophysical Journal Letters, and again I refer you to our group publications page.

I also use the Combined Array for Research in Millimeter Astronomy, or CARMA, shown above, and the The Caltech Submillimeter Observatory (the CSO is the silver dome in the background of the picture at the top of this page, to the right of the lava snowman). Through these studies, I investigate the chemical complexity of the interstellar medium, specifically the possibility of complex molecule formation on grains and the pathways leading to the formation of prebiotic molecules. I am collaborating with Professor Eric Herbst's group at The Ohio State University on chemical models of hot cores to explore the coupling between grain surface and gas phase reactions. In this model, photolysis of common ice constituents leads to the formation of radicals, which then become mobile on the grain surface during the warm-up phase of hot core formation. These radicals can then react to form a wide array of complex organic molecules. I am leading an effort to provide observational constraints for these models by investigating the physical and chemical environments of several hot cores. Preparatory work has recently been conducted with the new 4 GHz bandwidth receiver at the CSO, where 12 GHz of fully deconvolvable double sideband spectra of the Sgr B2(N-LMH) and Orion hot cores have recently been obtained . Previous studies have displayed the extended nature of many of the complex organics in this region, indicating a grain surface formation mechanism. The CSO survey may enable the identification of many new complex species in this star forming region. CARMA studies will be used to determine the spatial scale of these molecules, allowing accurate abundance determination for comparision to the hot core models.

Thesis Research

My thesis research in the group of Professor Geoffrey Blake at Caltech was an interdisciplinary study involving laboratory rotational spectroscopy and astronomical observations of several key prebiotic molecules. The laboratory work focused on obtaining the rotational spectra of the simplest three-carbon ketose sugar, 1,3-dihydroxyacetone, and its structural isomers methyl glycolate and dimethyl carbonate, as well as aminoethanol, the predicted interstellar precursor to alanine. The pure rotational spectral analysis of the low-lying torsional states of the simplest alpha-hydroxy aldehyde, glycolaldehyde, was also completed. The original Balle-Flygare Fourier transform microwave spectrometer was used to obtain the microwave spectra, while both the JPL and Caltech direct absorption flow cell spectrometers were used for additional direct absorption millimeter and submillimeter studies. To the left, Geoff and I are shown with the FTMW instrument on the day of first light after its move to Caltech, which was also the day of my candidacy exam!

The results of these laboratory experiments were used to guide observational searches with The Caltech Submillimeter Observatory, The Owens Valley Millimeter Array, and The Green Bank Telescope toward the hot core sources Sgr B2(N-LMH), Orion Hot Core/Compact Ridge, and W51 e1/e2. Evidence was found for the presence of dihydroxyacetone and methyl glycolate in Sgr B2(N-LMH), though additional observational searches since this orginal work have shown that these initial detected features are not likely due to these molecules. Regardless, these results of such searches have important implications for interstellar grain surface chemistry, and have led to adaptation of grain surface chemical models.

Undergraduate Honors Research

A massive extinction of more than 50 percent of existing life forms on Earth occurred 65 million years (Ma) ago. This event is marked in the geological record by the Cretaceous-Tertiary (KT) boundary and corresponds to the Chicxulub meteorite impact in the Yucatan Peninsula. Large quantities of reduced elemental carbon in the form of characteristic spheroidal clusters of soot have been found in twelve KT boundary sites from across the globe, indicating that deposition of soot was a global phenomenon. The source of this global soot layer is suspected to be eolian (airfall) deposition of fine-grained particles resulting from widespread wildfires.

My undergraduate honors thesis project with Professor Wendy Wolbach at IWU involved the analysis of numerous suites of meteorite impact-related samples for the presence of soot. These suites include samples from four KT boundary sites, namely the Madrid, Berwind, and Sussex sites from the North American Western Interior and Deep Sea Drilling Project Core 465-A from the Paleo-Pacific Basin. The mid-Pacific location of Core 465-A rules out soot deposition from groundwater runoff and indicates that eolian transport is the most probable mechanism for soot deposition. In addition to these KT boundary sites, I analyzed samples from several other meteorite impact sites in order to extend the theory of meteorite impact-related wildfires beyond KT boundary studies, setting limits on impact size requirements for soot formation. Additional projects included further study of elemental carbon isolation techniques in an attempt to refine carbon isolation methods for impact related samples of varying age and composition.

Publications

1. Widicus Weaver S. L., Wiczer M. B., Negru B., DiGangi J. P., Tom B. A., & McCall B. J. ``Continuous-wave cavity ringdown spectroscopy of the N₂⁺ Meinel System (2,1) band." J. Mol. Spectrosc., in press.
2. Widicus Weaver S. L., Remijan A. J., McMahon R. J., & McCall B. J. ``A search for ortho-benzyne (o-C₆H₄) in CRL 618." Astrophys. J. 671, L153-L156, 2007.
3. Garrod R. T., Widicus Weaver S. L., & Herbst E. ``Chemistry during the warm-up phase of a hot core: A new grain/gas chemical model." Astrophys. J., submitted.
4. Widicus Weaver S. L. & Blake G. A. ``1,3-Dihydroxyacetone in Sagittarius B2(N-LMH): The first interstellar ketose." Astrophys. J. 624, L33-L36, 2005.
5. Widicus Weaver S. L., Butler R. A. H., Drouin B. J., Petkie D. T., Dyl K. A., De Lucia F. C., & Blake G. A. ``Millimeter-wave and vibrational state assignments for the rotational spectrum of glycolaldehyde." Astrophys. J. Suppl. 158, 188-192, 2005.
6. Feldman M. T., Widicus S. L., Blake G. A., Kent D. R., & Goddard W. A. ``Aminomethanol water elimination: Theoretical examination." J. Chem. Phys. 123, 034304, 2005.
7. Widicus S. L., Braakman R., Kent D. R., & Blake G. A. ``The millimeter and submillimeter rotational spectrum of 1,3-dihydroxyacetone." J. Mol. Spectrosc. 224, 101-106, 2004.
8. Kent D. R., Widicus S. L., Blake G. A., & Goddard W. A. ``A theoretical study of the conversion of gas phase methanediol to formaldehyde." J. Chem. Phys. 119, 5117-5120, 2003.
9. Widicus S. L., Drouin B. J., Dyl K. A., & Blake G. A. ``Millimeter wavelength measurements of the rotational spectrum of 2-aminoethanol." J. Mol. Spectrosc. 217, 278-281, 2003.
10. Wolbach W. S., Widicus S., & Kyte F. T. ``A search for soot from global wildfires in Central Pacific Cretaceous-Tertiary boundary and other extinction and impact horizon sediments." Astrobiology 3, 91-97, 2003.

Conference Proceedings and Other Publications

1. Widicus Weaver S. L., Brumfield B. E., Howard S., Gmachl C., & McCall B. J. ``A laboratory and observational search for the vibrational spectrum of C₆₀." Proc. of: International Conference on Molecules in Space and Laboratory, 53, 2007.
2. Garrod R. T., Widicus Weaver S. L., & Herbst E. ``Complex molecules in star-forming regions - A (more) comprehensive gas-grain model." Proc. of: International Conference on Molecules in Space and Laboratory, 99, 2007.
3. Widicus Weaver S. L. & McCall B. J. ``Natural Fullerenes and Related Structures of Elemental Carbon'' J. Am. Chem. Soc. (book review), 129, 724, 2007.
4. Widicus S. L., Drouin B. J., Dyl K. A., & Blake G. A. ``Rotational spectroscopy and hot core observational astronomy of prebiotic molecules." Proc. of SFChem 2002: Chemistry as a Diagnostic of Star Formation, 449-451, 2003.
5. Wolbach W. S., Widicus S., & Dypvik H. ``A preliminary search for evidence of impact-related burning near the Mjølnir Impact Structure, Barents Sea." Lunar and Planetary Science Conference XXXII, 1332, 2001.
6. Wolbach W. S., Widicus S., & French B. M. ``Carbon-bearing impactites from the Gardnos Impact Structure, Norway: No evidence for soot." Lunar and Planetary Science Conference XXX, 1043, 1999.
7. Wolbach W. S., Widicus S., Moecker S. & Kyte F. T. ``Is the soot layer at the KT boundary really global?" Lunar and Planetary Science Conference XXIX, 1309, 1998.

Conference Presentations

1. Widicus Weaver S. L., Negru B., Wiczer M., DiGangi J. P., Tom B. A., & McCall B. J. ``Continuous-wave cavity ringdown study of the ¹⁴N₂⁺ Meinel System 2-1 band and the First Positive Band System of N₂^*." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
2. Widicus Weaver S. L., Mills A. A., & McCall B. J. ``Cavity Ringdown Spectroscopy of Molecular Ions in a Fast Ion Beam." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
3. Widicus Weaver S. L., Brumfield B. E., Mills A. A., Howard S. S., Gmachl C. F., & McCall B. J. ``A search for the 8.5 micron vibrational spectrum of C₆₀ in the laboratory and space." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
4. Widicus Weaver S. L., Garrod R. T., & Herbst E. ``A new model for complex chemistry in hot cores." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
5. Widicus Weaver S. L., Remijan A. J., McMahon R. J., & McCall B. J. ``A Green Bank Telescope search for ortho-benzyne in CRL 618." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
6. Brumfield B. E., Widicus Weaver S. L., Howard S. S., Gmachl C. F., & McCall B. J. ``Cavity ringdown spectrum of the ν₈ band of methylene bromide using a quantum cascade laser." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
7. Mills A. A., Widicus Weaver S. L., & McCall B. J. ``Development of a fast ion beam spectrometer for molecular ion spectroscopy." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
8. Kuo H.-L., Friedel D. N., Looney L. W., Snyder L. E., Widicus Weaver S. L., & McCall B. J. ``Preparation for the astronomical search for protonated methanol." 62nd Ohio State University International Symposium on Molecular Spectroscopy, 2007.
9. Widicus Weaver S. L., Brumfield B. E., Howard S., Gmachl C., & McCall B. J. ``A laboratory and observational search for the vibrational spectrum of C₆₀." International Conference on Molecules in Space and Laboratory, 2007.
10. Garrod R. T., Widicus Weaver S. L., & Herbst E. ``Complex molecules in star-forming regions - A (more) comprehensive gas-grain model." International Conference on Molecules in Space and Laboratory, 2007.
11. Widicus Weaver S. L., Garrod R. T., Herbst E. ``A new model for complex chemistry in hot cores." Enrico Fermi Institute Mini-Symposium on Interstellar Molecules, 2007.
12. Negru B., Wiczer M., Widicus Weaver S. L., DiGangi J. P., Tom B. A., & McCall B. J. ``Infrared absorption spectroscopy of the ¹⁴N₂⁺ Meinel System 2-1 band (poster)." American Chemical Society National Meeting 233, 2007.
13. Widicus Weaver S. L., Mills A. A., & McCall B. J. ``Continuous-wave cavity ringdown spectroscopy of molecular ions in a fast ion beam (poster)." American Chemical Society National Meeting 233, 2007.
14. Brumfield B. E., Widicus Weaver S. L., Howard S. S., Gmachl C. F., & McCall B. J. ``Continuous wave cavity ringdown spectroscopy of C₆₀ at 8.5 micron using a quantum cascade laser and a supersonic expansion source (poster)." American Chemical Society National Meeting 233, 2007.
15. Widicus Weaver S. L., Zwier M. C., Ding Y., & McCall B. J. ``Laboratory and observational studies of C₆₀ and C₆₀⁺." American Chemical Society National Meeting 231, 2006.
16. Sumner M. C., Blake G. A., Harris A. I., Leong M., Phillips T. G., Rice F., Widicus Weaver S., Yoshida H., & Zmudzinas J. ``Millimeter line surveys of Class 0 protostars and targeted searches for complex organics in high mass star-forming regions (poster)." Protostars and Planets V, 2005.
17. Widicus Weaver S. L., Kelley M. J., & Blake G. A. ``Complex chemistry on interstellar grains (poster)." International Astronomical Union Symposium 231: Astrochemistry - Recent Successes and Current Challenges, 2005.
18. Widicus Weaver S. L. & Blake G. A. ``The rotational spectra of the internal rotors methyl glycolate and dimethyl carbonate, structural isomers of the 3C sugars." 60th Ohio State University International Symposium on Molecular Spectroscopy, 2005.
19. Widicus Weaver S. L. & Blake G. A. ``Reconsidering radical-radical reactions on grain surfaces: A new interstellar chemical model." 60th Ohio State University International Symposium on Molecular Spectroscopy, 2005.
20. Braakman R., Drouin B., Widicus S. L. & Blake G. A. ``The rotational spectrum and observational study of hydroxyacetone." 60th Ohio State University International Symposium on Molecular Spectroscopy, 2005.
21. Widicus S. L. & Blake G. A. ``Detection of dihydroxyacetone in Sgr B2(N-LMH): The first 3C interstellar sugar?" 59th Ohio State University International Symposium on Molecular Spectroscopy, 2004.
22. Widicus S. L., Drouin B. J., & Blake G. A. ``The FT-microwave spectrum of dimethyl carbonate." 59th Ohio State University International Symposium on Molecular Spectroscopy, 2004.
23. Widicus S. L., Braakman R., & Blake G. A. ``3C sugars in interstellar hot cores? Studies of the laboratory rotational spectrum of dihydroxyacetone." 58th Ohio State University International Symposium on Molecular Spectroscopy, 2003.
24. Widicus S. L., Dyl K. A., & Blake G. A. ``Microwave, millimeter, and submillimeter spectroscopy of prebiotic interstellar molecules (poster)." 50th Annual Western Spectroscopy Association Conference, 2003.
25. Widicus S. L., Drouin B. J., Dyl K. A., & Blake G. A. ``Rotational spectroscopy and hot core observational astronomy of prebiotic molecules (poster)." SFChem 2002: Chemistry as a Diagnostic of Star Formation, 2002.
26. Widicus S. L., Drouin B. J., Dyl K. A., & Blake G. A. ``Rotational spectroscopy and hot core observational searches for aminoethanol (poster)." Astrobiology Science Conference, 2002.
27. Widicus S. L., Drouin B. J., Dyl K. A., & Blake G. A. ``The rotational spectrum of amino-ethanol." 57th Ohio State University International Symposium on Molecular Spectroscopy, 2002.
28. Wolbach W. S., Widicus S. & Dypvik H. ``A preliminary search for evidence of impact-related burning near the Mjølnir Impact Structure, Barents Sea (poster)." 32nd Lunar and Planetary Science Conference, 2001.
29. Widicus S., Wolbach W. S., & Nelson B. ``Chemical techniques for the isolation of elemental carbon from sediments (poster)." American Chemical Society National Meeting 220, 2000.
30. Wolbach W. S., Widicus S., & French B. M. ``Carbon-bearing impactites from the Gardnos Impact Structure, Norway: No evidence for soot (poster)." 30th Lunar and Planetary Science Conference, 1999.
31. Wolbach W. S., Widicus S., Moecker S., & Kyte F. T. ``Is the soot layer at the KT boundary really global? (poster)" 29th Lunar and Planetary Science Conference, 1998.

Awards and Other Distinctions

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