We have recently constructed a time-domain TeraHertz (THz) spectrometer for the study of molecular ices in the far-infrared. Here, we present the results of a study of amorphous and crystalline ices of simple alcohols from methanol (CH₃OH) through butanol (CH₃(CH₂)₃OH) in the region of 0.3 - 7.5 THz. We examine the effects of the length and degree of branching of the carbon chain on the observed spectra arising from the bulk, large-amplitude motions which are prominent in this spectral region. We also discuss these results in an astrochemical context: the application of these spectra to astronomical observations of interstellar ices with Herschel PACS/SPIRE and SOFIA.

It is generally accepted that complex organic molecules (COMs) form on the icy surface of interstellar grains. Our ability to identify interstellar complex species in the ices is affected by the limited number of laboratory analogs that can be compared to the huge amount of observational data currently coming from international astronomical facilities, such as the Herschel Space Observatory, SOFIA, and ALMA. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar ice analogs in a range that fully covers the spectral bandwidth of the aforementioned facilities (0.3 – 7.5 THz). The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 – 500 cm⁻¹). This talk focuses on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H₂O, CO₂, CO, CH₃OH, NH₃, and CH₄) compared to more complex molecules (e.g., HCOOH, CH₃COOH, CH₃CHO, (CH₃)₂CO, HCOOCH₃, and HCOOC₂H₅). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice database, which will allow quantitative studies of the ISM, and potentially guide future astronomical observations of species in the solid phase.

Polycyclic aromatic hydrocarbons (PAHs) present themselves as a strong candidate as carriers of the unidentified infrared features (UIRs). As UIR carriers, PAHs may account for up to 20% of the interstellar carbon budget and may play key roles in many chemical and physical processes in the ISM, and yet our inability to definitively detect PAHs hinders our ability to evaluate the role they may play. A possible solution is observations in the TeraHertz (THz) regime, where observed transitions are specific to each molecule. Recent advances in THz technology have enabled both laboratory spectroscopy and astronomical observations in this region. A first step in both laboratory and astronomical studies of PAHs is the acquisition of spectra of pure PAH samples. Here, we present the THz time-domain spectra (0.3 - 7 THz) of several PAHs, including naphthalene, anthracene, and pyrene, and discuss the utility of these spectra for future laboratory and astronomical studies.

Chemical reactions involving the icy mantles of interstellar dust grains have been invoked in astrochemical models to explain the formation of complex organic molecules in interstellar clouds. Interstellar ices can act as a substrate to encourage reactions in three ways: reactions within the bulk ice, reactions between mobile species on the ice surface, or gas-phase reactions that are initiated by thermal desorption or photodesorption of the ice. We are building a new experiment that uses millimeter/submillimeter absorption spectroscopy to probe the gas-phase chemistry directly above the ice surface during thermal- or photo-processing. We will present the experimental design and preliminary results for pure water ices and water+ methanol ice mixtures.

Astrochemical models of interstellar chemistry predict the formation of many complex molecules of prebiotic interest, including aminomethanol (HOCH₂NH₂). Aminomethanol has been proposed as the gas-phase interstellar precursor to glycine, the simplest amino acid, in star-forming regions. Aminomethanol is therefore a potential tracer of prebiotic interstellar chemistry. However, the laboratory spectrum of aminomethanol remains elusive because it is unstable under typical laboratory conditions. A new (sub)millimeter spectrometer is being used to study the reaction between O(¹D) and methylamine to form aminomethanol. O(¹D) is produced via laser photolysis of ozone in a fused silica tube, where it reacts with methylamine before a supersonic expansion. The insertion reaction of O(¹D) with methylamine to form aminomethanol is highly exothermic, leading to a mixture of additional reaction products that have been identified through their rotational spectroscopic signatures. Here we will present the experimental setup, observed reaction products, and initial results towards the characterization of aminomethanol. Comparisons will also be made with observational spectra from several star-forming regions.

For cool stellar and substellar objects, atomic lines weaken, and detailed elemental and isotopic abundances are often derived from molecular absorption features. We have embarked on a project to provide molecular line lists by combining experimental observations for line positions with ab initio calculations for line strengths. So far we have results for MgH (A-X and B-X transitions)¹², C₂ (Swan system)³⁴, CN (red and violet systems)⁵, CP (A-X transition)⁶, NH (vibration-rotation bands) and OH (Meinel system)⁷. This talk will briefly describe the new line lists for the Swan system (d³Π-a³Π) of C₂ and ¹²C¹³C, and the red (A²Π-X²Σ⁺) and violet (B²Σ⁺-X²Σ⁺) systems of CN, ¹³CN and C¹⁵N. Applications to the spectra of carbon-enhanced metal-poor stars, the K-giant Arcturus, the metal-rich open cluster NGC 6791, the Sun and comets will be presented.
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¹E. GharibNezhad, A. Shayesteh and P. F. Bernath, Mon. Notices R. Astro. Soc. 432, 2043-2047 (2013) ²K. H. Hinkle, L. Wallace, R. S. Ram, P. F. Bernath, C. Sneden and S. Lucatello, Astrophys. J. Suppl. 207, 26 (7pp) (2013) ³J. S. A. Brooke, P. F. Bernath, T. W. Schmidt and G. B. Bacskay, J. Quant. Spectrosc. Rad. Trans. 124, 11-20 (2013) ⁴R. S. Ram, J. S. A. Brooke, P. F. Bernath, C. Sneden and S. Lucatello, Astrophys. J. Suppl. 211, 5 (7pp) (2014) ⁵J. S. A. Brooke, R. S. Ram, C. M. Western, G. Li, D. W. Schwenke and P. F. Bernath, Astrophys. J. Suppl. 210, 23 (15pp) (2014) ⁶R. S. Ram, J. S. A. Brooke, C.M. Western and P. F. Bernath, J. Quant. Spectrosc. Rad. Transfer (in press) ⁷J. S. A. Brooke et al., this meeting, P301

Ions and radicals are important in astrochemical models because they act as key reaction intermediates in the interstellar medium. However, much laboratory work remains to determine the rotational spectra of most ions and radicals of astrophysical interest. This is especially true in the millimeter/submillimeter range, where small sample quantities limit spectral signal intensities. Hollow-cathode discharges have previously been used to create and study ions and radicals of astrophysical interest, but most of these instruments have been coupled with infrared spectrometers. We have developed a hollow-cathode spectrometer to investigate ions and radicals using (sub)millimeter spectroscopy. Spectrometer performance has been benchmarked using the N₂H⁺ molecular ion, which has a known rotational spectrum. Initial results from these benchmarking studies, as well as new spectral results for other molecular targets, will be presented.

Glycolic acid, HOCH₂COOH is the simplest α-hydroxy acid. It is as yet undetected in the interstellar medium, but is known to be present in carbonaceous meteorites and in residues from UV-photolysed interstellar ice analogue mixtures. Prior rotational spectroscopy has been carried out up to 40 GHz for the main, SSC conformer, ^1,2 and up to 72 GHz for the weaker, AAT, conformer.³
Presently we report the analysis of the rotational spectrum of glycolic acid on the basis of broadband measurements performed up to 318 GHz, and updated spectroscopic constants for the ground state and the first two excited states of the low-frequency ν₂₁ torsional mode. We have used the AABS package to assign multiple further excited vibrational states of the SSC conformer. In particular, we have been able to assign the highly perturbed triad of ν₁₄, ν₂₀ and 3ν₂₁ states. The triad has been fitted down to experimental accuracy with a coupled fit, which allowed us to pin down the hitherto elusive frequency of the ν₂₁ mode. The experimental results make an interesting comparison with those of anharmonic force field calculations. We have also been able to extend the measurements for the AAT conformer.
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¹C.E.Blom, A.Bauder, Chem. Phys. Lett., 82, 492 (1981), J. Am. Chem. Soc., 104, 2993 (1982). ²H.Hasegawa, O.Ohashi, I.Yamaguchi, J. Mol. Spectrosc., 82, 205 (1982). ³P.D.Godfrey, F.M.Rodgers, R.D.Brown, J. Am. Chem. Soc., 119, 2232 (1997).

Urea is an important terrestrial bio-molecule, which has been tentatively detected in the interstellar medium ¹. To match the much improved range and sensitivities of modern sub-millimeter telescopes a broad laboratory assay of rotational transitions needs to be recorded in order to aid in the definitive identification of this molecule. This paper focuses on the spectroscopic assignment of the rotational transitions of urea in the 207-500 GHz range which belong to its ground and first excited vibrational states.
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¹Remijan, A.J., L.E. Snyder, B.A. McGuire, H.-L. Kuo, L.W. Looney, D.N. Friedel, G.Y. Golubiatnikov, F.J. Lovas, V.V. Ilyushin, E.A. Alekseev, S.F. Dyubko, B.J. McCall, and J.M. Hollis, Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [NH22CO]. The Astrophysical Journal, 2014. 783(2): p. 77

The urea molecule, (NH₂)₂CO, has a complex potential energy surface resulting from a combination of the NH₂ torsion and NH₂ inversion motions. This leads to a distribution of lowest vibrational states that is expected to be significantly different from the more familiar picture from simple inversion or normal mode models.^1,2
The broadband 207-500 GHz spectrum of urea recorded in Dayton has signal to noise sufficient for assignment of rotational transitions in excited vibrational states up to at least 500 cm⁻¹. In addition to the previously reported analysis of the ground and the lowest excited state we have been able to assign transitions in at least five other excited vibrational states. Strongly perturbed transitions in a close doublet of such states have been fitted to within experimental accuracy with a coupled fit and a splitting in the region of 1 cm⁻¹. These assignments combined with vibrational energy estimates from relative intensity measurements allow for empirical discrimination between different models for the energy level manifestation of the large amplitude motions in urea.^b
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¹P.D.Godfrey, R.D.Brown, A.N.Hunter J. Mol. Struct., 413-414, 405-414 (1997). ²N.Inostroza, M.L.Senent, Chem. Phys. Lett., 524, 25 (2012).

Polycyclic Aromatic Hydrocarbons (PAHs) have long been suspected to be the carriers of so called Unidentified Infrared Bands (UIBs).¹ Most of the results published in the literature report rotationally unresolved spectra of pure carbon as well as heteroatom-containing PAHs species. To date for this class of molecules, the principal source of rotational informations is ruled by microwave (MW) spectroscopy ² while high resolution measurements reporting rotational structure of the infrared (IR) vibrational bands are very scarce. Recently, some high resolution techniques provided interesting new results to rotationally resolve the IR and far-IR bands of these large carbonated molecules of astrophysical interest.³ One of them is to use the bright synchrotron radiation as IR continuum source of a high resolution Fourier transform (FTIR) spectrometer. We report the very complementary analysis of the [1,6] naphthyridine (a N-bearing PAH) for which we recorded the microwave spectrum at the PhLAM laboratory (Lille) and the high resolution far-infrared spectrum on the AILES beamline at synchrotron facility SOLEIL. MW spectroscopy provided highly accurate rotational constants in the ground state to perform Ground State Combinations Differences (GSCD) allowing the analysis of the two most intense FT-FIR bands in the 50-900 cm⁻¹ range. Moreover, during this presentation the negative value of the inertial defect in the GS of the molecule will be discussed.
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¹A. Leger, J. L. Puget, Astron. Astrophys. 137, L5-L8 (1984); L. J. Allamandola et al. Astrophys. J. 290, L25-L28 (1985). ²Z. Kisiel et al. J. Mol. Spectrosc. 217, 115 (2003); S. Thorwirth et al. Astrophys. J. 662, 1309 (2007); D. McNaughton et al. J. Chem. Phys. 124, 154305 (2011). ³S. Albert et al. Faraday Discuss. 150, 71-99 (2011); B. E. Brumfield et al. Phys. Chem. Lett. 3, 1985-1988 (2012); O. Pirali et al. Phys. Chem. Chem. Phys. 15, 10141 (2013).

Astronomical observation of dimethyl ether,¹ methyl ethyl ether² and vinyl alcohol³ places the methyl vinyl ether among the species of potential interstellar relevance. The millimeter and submillimeter-wave transitions pertaining to the vibrational ground state and the first excited states of the methoxy, ν₂₄, and methyl, ν₂₃, torsional modes and the in-plane bending mode, ν₁₆, of the cis-methyl vinyl ether have been measured and analyzed in the frequency region from 50 to 600 GHz. A significant Fermi-type and Coriolis interactions between the v₂₄=1 and v₂₃=1 states have been observed and the rotational spectra were analyzed using an effective two-state Hamiltonian explicitly involving corresponding coupling operators. A sets of spectroscopic constants for the ground state as well as for all three excited states reproducing the observed spectrum within the experimental uncertainty provide sufficiently precise information for the astronomical search for methyl vinyl ether.
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¹Z. Peeters, S. D. Rodgers, S. B. Charnley, L. Schriver-Mazzuoli, A. Schriver, J. V. Keane, and P. Ehrenfreund, Astron. & Astrophys. 2006, 445, 197. ²G. W. Fuchs, U. Fuchs, T. F. Giesen, F. Wyrowski, Astron. & Astrophys. 2005, 444, 521. ³B. E. Turner, A. J. Apponi, Astrophys. J. Lett. 2001, 561, 207.