At present, more than 160 different chemical species have been detected in interstellar space, primarily in giant gas clouds located throughout our Galaxy and in gaseous material surrounding old stars, but also in other unusual environments, as illustrated in Figure 1. Despite the extreme conditions of the so-called interstellar medium (ISM), which is typically quite cold (T ~ 10-50 K) and very diffuse (n ~ 10³ - 106 particles/cc), chemistry flourishes, producing quite common, but often exotic, compounds, including many reactive radicals and molecular ions, ranging in size from simple diatomics like CO to complex species like C60. It is now recognized that we live in a molecular universe, and that interstellar molecular material is continuously recycled in the ISM. The life cycle is shown in Figure 1. Molecules form in dying stars, and then are passed on theough the planetary nebula stage and into the diffuse ISM. This matter subsequently collapses to form dense clouds, the sites of star and solar systems. The stars eventually die, and the cycle repeats. As solar systems form, some of the pristine molecular material from the nascent molecular cloud is delivered to young planet surfaces via comets, meteorites, and interplanetary dust particles. This material is thought to have influenced early biochemistry, thus tracing life's originss back to interstellar space.
Figure 1: The interstellar molecular life cycle, tracing molecular formation from the ejecta of dying stars into the diffuse, and then dense ISM, and subsequently into regions of star and solar system formation via the protoplanetary disk stage. Some of the pristine interstellar molecular matter is the delivered to planet surfaces via bombardment by comets, meterorites, and interplanetary dust particles.
The primary objective of research in the Ziurys group is to understand the molecular life cycle and study the chemistry occurring in the vast regions of space via an interdisciplinary approach that involves high resolution molecular spectroscopy in the laboratory and radio astronomical observations. The University of Arizona is unique in this regard as it has its own radio telescopes, operated by the Arizona Radio Observatory (ARO), which can be used for graduate research. Radio telescopes are used to measure rotational molecular spectra and identify new chemical compounds by their "fingerprint" signatures, which are known from laboratory measurements. We are interested in discovering what chemical compounds exist in space and in which types of interstellar sources, how they are formed, and how this impacts the origins of solar systems and planets, and ultimately life. As shown in Figure 2, many interstellar objects are have very dense and complicated radio spectra, illustrating the complexity of their chemistry. Displayed in this figure is a "spectrum" of the cloud Sagitarrius B2N, which is located near the center of our Galaxy. Over the wavelngth region 68 - 280 GHz, over 15,000 spectral lines are present, a large fraction which are unidentified. Possible carriers of these unidentified lines are smaller species containing metals such as iron, magnesium, and chromium; (also significant for organometallic chemistry), organic molecules related to sugars and nucleic acids, and phosphorus-bearing compounds.
Figure 2: The millimeter-wave spectrum (68 - 280 GHz) of the molecular cloud Sagitarrius B2N, showing over 15,000 individual spectral emission and absorption lines, many which are unidentfied. Thses data were obtained with the telecopes of the Arizona Radio Observatory.
Laboratory studies focus on the measurement of gas-phase rotational spectrum of species of astrophysical interest in the microwave, millimeter and THz regions of the electromagnetic spectrum (~3 GHz - 1.5 THz). This goal requires design and construction of our own spectrometer systems, as shown in Figure 3. Currently, there are four working instruments in the Ziurys group: two mm/sub-mm direct absorption systems, a velocity-modulation spectrometer specifically designed to study molecular ions, and a pulsed, Fourier transform microwave/mm-wave (FTMmmW) machine. Part of the laboratory work also concerns developing exotic synthetic techniques for creating these transient species in detectable concentrations including electrical discharges and laser ablation. We have succeeded in recording the spectra of a wide range of metal-bearing species, in particular radicals and, more recently, ions, such as FeCN, ScC2,FeCO+,CrCCH, FeO+, and ClZnCH3. Many of these species have unpaired electrons, and thus their spectra exhibit complex fine and hyperfine splittings (see Figure 4). Analysis of such data requires a detailed knowledge of quantum mechanics. Other investigations include possible pre-biotic species such as EtNH2 and methylisocyanate hydroxyacetone. The fingerprints measured in the laboratory enable such species to be identified in space.
Figure 3: Two of the spectrometers of the Ziurys group: Left: Fourier transform microwave/mm-wave system, with the laser ablation source. Right: The velocity modulation spectrometer showing the purple glow of the AC discharge.
Figure 4: Laboratory spectra of the ScO radical in its X2SIGMA state. Left: FTmmW data showing six scandium hyperfine components. Right: Millimeter-wave direct absorption spectra.
Observational studies in the Ziurys group include the identification of new interstellar species, such as FeCN, AlO, AlOH, CCN, and PO, which is usually conducted in conjunction with laboratory work. The newest molecule found by the Ziurys Group is CH3NCO, which was identified in the spectral survey data of SgrB2N. Other projects involve elucidating the chemistry associated with evolved stars, such as VY Canis Majoris, and the survival of molecules in planetary nebulae such as the Helix. Observations are also currently being conducted to trace the history of carbon and organic chemistry through the molecular life cycle, as shown in Figure 1.
Figure 5: The Submillimeter Telescope (SMT) of the Arizona Radio Observatory, located at Mt. Graham, AZ (left), and the new ALMA prototype 12-meter telescope at Kitt Peak (right).
Interstellar molecules are primarily studied using the telescopes of the Arizona Radio Observatory (ARO). ARO operates the Submillimeter Telescope (SMT) on Mount Graham, AZ, and the new 12-meter (12m) Telescope at Kitt Peak (see Figure 4). The new 12m is built with the most advanced technology for radio telescopes. It was one of the three prototype antennas built and tested for the Atacama Large Millimeter Array (ALMA), and became property of the UA on March 23, 2013. The surface is made of rhodium coated panels, while the structure is formed from carbon fiber.
Interstellar Detection of Methyl Isocyanate CH3NCO in Sgr B2(N): A Link from Molecular Clouds to Comets,” D.T. Halfen, V.V. Ilyushin, and L.M. Ziurys, Ap.J (Letters), 812, L5 (2015).
“Prebiotic Chemical Evolution in the Astrophysical Context,” L.M. Ziurys, G.R. Adande, J.L. Edwards, D.R. Schmidt, D.T. Halfen, and N.J. Woolf, Origins of Life and the Evolution of the Biosphere, 45, 275 (2015).
"The Millimeter-Wave Spectrum of CCN (X2Πr): A Combined Fourier Transform and Direct Absorption Study,” J.K. Anderson, D.T. Halfen, and L.M. Ziurys, J. Mol. Spectrosc., 305, 1 (2015).
Millimeter/Sub-mm Spectroscopy of PH2CN (X̃ 1A′) and CH3PH2 (X̃ 1A′): Probing the Complexity of Interstellar Phosphorus Chemistry,” D.T. Halfen, D.J. Clouthier, and L.M. Ziurys, Ap.J., 796, 36 (2014).
Detection of CCN (X2Πr) in IRC +10216: Constraining Outer-Envelope Carbon-Chain Chemistry,” J.K. Anderson and L.M. Ziurys, Ap.J. (Letters), 795, L1 (2014).
"Fourier Transform Microwave/Millimeter-wave Spectroscopy of the ScC2 (X2A1) Radical: A Model System for Endohedral Metallofullerenes," J.Min, D.T. Halfen, and L.M. Ziurys, Chem. Phys. Lett., 609, 70 (2014).
"Millimeter Observations of CS, HCO+, and CO Towards Five Planetary Nebulae: Following Molecular Abundance with Nebular Age," J.L. Edward, E.G. Cox, and L.M. Ziurys, Ap.J., 791, 79 (2014).
"The Helix Nebula Viewed in HCO+: Large Scale Mapping of the J = 1 → 0 Transition," N.R. Zeigler, L.N. Zack, N.J. Woolf, and L.M. Ziurys, Ap.J., 778, 16 (2013).
"The Remarkable Molecular Content of the Red Spider Nebula (NGC 6537)," J.L. Edwards and L.M. Ziurys, Ap.J. (Letters), 770, L5 (2013).
"Insights into Surface Hydrogenation in the Interstellar Medium: Observations of Methanimine and Methyl Amine in Sgr B2(N)," D.T. Halfen, V.V. Ilyushin, and L.M. Ziurys, Ap.J., 767, 66 (2013).
"The Fourier Transform Microwave Spectrum of YC2 (X2A1) and its 13C Isotopologues: Chemical Insight into Metal Dicarbides," D.T. Halfen, J.Min, and L.M. Ziurys, Chem. Phys. Lett., 555, 31 (2013).
"Observations of Interstellar Formamide: Availability of a Prebiotic Precursor in the Galactic Habitable Zone," G.R. Adande, N.J. Woolf, and L.M. Ziurys, Astrobiology, 13, 439 (2013).
"Chemical Complexity in the Helix Nebula: Multi-Line Observations of H2CO, HCO+, and CO," L.N. Zack and L.M. Ziurys, Ap.J., 765, 112 (2013).
"Gas-Phase Rotational Spectroscopy of AlCCH (X¹Σ+): A Model System for OrganoAluminum Compounds," M. Sun, D. T. Halfen, J. Min, D. J. Clouthier, and L. M. Ziurys, Chem. Phys. Lett., 553, 11 (2012).
"The Microwave and Millimeter Rotational Spectrum of the PCN Radical (X³Σ-)," D.T. Halfen, M. Sun, D.J. Clouthier, and L.M. Ziurys, J. Chem. Phys., 136, 144312 (2012).
"The Microwave and Millimeter Spectrum of ZnCCH (X²Σ+): A New Zinc-Containing Free Radical," J. Min, D. T. Halfen, M. Sun, B. Harris and L. M. Ziurys, J. Chem. Phys., 136, 244310 (2012).
"A Millimeter-Wave Observations of CN and HCN and their 15N Isotopologues: A New Evaluation of the 14N/15N Ratio Across the Galaxy," G.R. Adande and L.M. Ziurys, Ap.J., 744, 194 (2012).
"Gas-Phase Synthesis and Structure of Monomeric ZnOH: A Model Species for Metalloenzymes and Catalytic Surfaces," L.N. Zack, M. Sun, M.P. Bucchino, D.J. Clouthier, and L.M. Ziurys, J. Phys. Chem., 1542, 50 (2012).
"Millimeter-Wave Rotational Spectroscopy of FeCN (X4Δi) and FeNC (X6Δi): Determining the Lowest Energy Isomer," M.A. Flory and L.M. Ziurys, J. Chem. Phys., 135, 184303 (2011).
"Formation of Peptide Bonds in Space: A Comprehansive Study of Formamide and Acetamide in SgrB2(N)," D.T. Halfen, V. Ilyushin, and L.M. Ziurys, Ap.J., 743, 60 (2011).
"Iron-Containing Molecules in Circumstellar Envelopes: Detection of FeCN (X4Δi) in IRC+10216," R.L. Pulliam, J.L. Edwards and L.M. Ziurys, Ap.J. (Letters), 733, L36 (2011).
"Circumstellar Ion-Molecule Chemistry: Observations of HCO+ in the Envelopes of O-Rich Stars and IRC+10216," R.L. Pulliam, J.L. Edwards, and L.M. Ziurys, Ap.J., 743, 36 (2011).
"Fourier-Transform Microwave Spectroscopy of FeCN (X4Σi): Confirmation of the Quartet Electronic Ground State," L.N. Zack, J. Min, B.J. Harris, M.A. Flory, and L.M. Ziurys, Chem. Phys. Letters, 514, 202 (2011).
"Observations of the [HNCS]/[HSCN] Ratio in the SgrB2 and TMC-1: Evidence for Low Temperature Gas-Phase Chemistry," G.R. Adande, D.T. Halfen, L.M. Ziurys, D. Quan, and E. Herbst, Ap.J., 725, 651 (2010).
"The Rotational Spectrum of CuCCH (X¹Σi): A Fourier Transform Microwave DALAS and Millimeter/Submillmeter Study," M. Sun, D.T. Halfen, J. Min, B. Harris, D.J. Clouthier, and L.M. Ziurys, J. Chem. Phys., 133, 174301 (2010).
"Activation of CH4 by Zinc: Gas-Phase Synthesis, Structure, and Bonding in HZnCH3," M.A. Flory, A.J. Apponi, L.N. Zack, and L.M. Ziurys, J. Am. Chem. Soc., 132, 17186 (2010).
"The Arizona Radio Observatory 1mm Spectral Survey of IRC+10216 and VY Canis Majoris," E.D. Tenenbaum, J.L. Dodd, S.N. Milam, N.J. Woolf, and L.M. Ziurys., Ap.J. Suppl., 190, 348 (2010).
"Millimeter/Submillimeter Velocity Modulation Spectroscopy of FeO+ (X6Σ+): Characterizing Metal Oxide Cations," D.T. Halfen and L.M. Ziurys, Chem. Phys. Letter, 496, 8 (2010).
"Exotic Metal Molecules in Oxygen-Rich Envelopes: Detection of AlOH (X¹Σ+) in VY Canis Majoris," E.D. Tenenbaum and L.M. Ziurys, Ap.J. (Letter), 712, L93 (2010).