We present a brief overview of the recently established laboratory astrophysics group in Kassel/Germany with a focus on our THz technology. After an outline of our laboratory equipment and recent projects the talk will focus on our new fast spectral scan technique for molecular jet experiments. Here, a new test setup for broadband fast sweep spectrometry in the MW to submm wavelength region has been realized and can be applied to identify transient molecules in a supersonic jet. An arbitrary waveform generator (AWG) is used to generate chirped pulses with a linear frequency sweep in the MHz regime. Pulse durations are of a few microseconds. These pulses are up-converted in frequency, e.g. into the 50 GHz microwave frequency range utilizing a synthesizer, or using a synthesizer plus standard amplifier multiplier chain (AMC) to reach the 100-300 GHz region. As test, NH₃ has been measured between 18-26 GHz in a supersonic jet of 500 μs duration. Acetonitrile (CH₃CN) was tested in the (90-110) GHz range. The spectrometer is capable of providing fast, broadband and low-noise measurements. Experiments with non-stabel molecular production conditions can greatly benefit from these advantages. The setup enables the study of Van-der-Waals-clusters, as well as carbon chain molecules and small metal-containing refractory molecules when combined with appropriate molecule sources.

The discovery of extrasolar planets is one of the major scientific advances of the last two decades. Thousands of planets have now been detected and astronomers are beginning to characterize their composition and physical characteristics. To do this requires a huge quantity of spectroscopic data most of which are not available from laboratory studies. The ExoMol project [1] is generating a comprehensive solution to this problem by providing spectroscopic data on all the molecular transitions of importance in the atmospheres of exoplanets. These data are widely applicable to other problems such studies on cool stars, brown dwarfs and circumstellar environments as well as industrial and technological problems on earth. ExoMol employs a mixture of first principles and empirically tuned quantum mechanical methods to compute comprehensive and very large rotation–vibration and rovibronic line lists. Results span a variety of closed (NaH, SiO, PN, NaCl, KCl, CS) and open (BeH, MgH, CaH, AlO, VO) shell diatomics to triatomics (HCN/HNC, SO₂, H₂S, H₃⁺), tetratomics (H₂CO, PH₃, SO₃, H₂O₂), plus methane [2] and nitric acid [3]. This has led directly to the detection of new species in the atmospheres of exoplanets [4]. A new comprehensive data release has just been completed [5]. Progress on and future prospects of the project will be summarised.

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J. Tennyson, S. N. Yurchenko, Mon. Not. R. astr. Soc., 425, 21, 2012.

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S. N. Yurchenko, J. Tennyson, J. Bailey, M. D. J. Hollis, G Tinetti, Proc. Nat. Acad. Sci., 111, 9379, 2014.

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A. I. Pavlyuchko, S. N. Yurchenko, J. Tennyson, Mon. Not. R. astr. Soc., 452, 1702, 2015.

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A. Tsiaras et al, Astrophys. J., in press. [5] J. Tennyson et al, J. Mol. Spectrosc., in press.

Methane is one of the many hydrocarbons that is found in cool planetary atmospheres in our solar system. Its prominence also extents to hot sub-stellar environments such as brown dwarfs and hot Jupiter exoplanets. High resolution transmission spectra (0.02 cm⁻¹) have been recorded at eight different temperatures (between 294 - 1000 K) within the 1 - 2 μm region using a Fourier transform infrared spectrometer and tube furnace. From these observations, temperature dependent empirical line lists have been produced that include line position, intensity, lower state energy and possible quantum number assignments. Our line lists and spectra can be used to directly simulate the atmospheric spectra of brown dwarfs and exoplanets. These experimental line lists are also compared to predictions from ab initio variational calculations that are known to have diminished accuracy in the 1 - 2 μm region.

For many years, scientists suspected that the interstellar medium was too hostile for organic species and that only a few simple molecules could be formed under such extreme conditions. However, the detection of approximately 180 molecules in interstellar or circumstellar environments in recent decades has changed this view dramatically. A rich chemistry has emerged, and relatively complex molecules such as C₆₀ and C₇₀ are formed. Recently, researchers have also detected complex organic and potentially prebiotic molecules, such as amino acids, in meteorites and in other space environments. Those discoveries have further stimulated the debate on the origin of the building blocks of life in the universe. Rotational spectroscopy plays a crucial role in the investigation of planetary atmosphere and the interstellar medium. Increasingly these astrochemical investigations are assisted by quantum-mechanical calculations of structures as well as spectroscopic and thermodynamic properties to guide and support observations, line assignments, and data analysis in these new and chemically complicated situations.V. Barone, M. Biczysko, C. Puzzarini 2015, Acc. Chem. Res., 48, 1413owever, it has proved challenging to extend accurate quantum-chemical computational approaches to larger systems because of the unfavorable scaling with the number of degrees of freedom (both electronic and nuclear). In this contribution, it is demonstrated that it is now possible to compute physicochemical properties of building blocks of biomolecules with an accuracy rivaling that of the most sophisticated experimental techniques. We analyze the spectroscopic properties of representative building blocks of DNA bases (uracil and thiouracil), of proteins (glycine and glycine dipeptide analogue), and also of PAH (phenalenyl radical and cation).

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Footnotes:

V. Barone, M. Biczysko, C. Puzzarini 2015, Acc. Chem. Res., 48, 1413H

In this talk, the quantum chemistry of astronomically relevant molecules will be outlined with an emphasis on the structures and energetics of C₇H₂ isomers, which are yet to be identified in space. Although more than 100’s of isomers are possible for C₇H₂, to date only 6 isomers had been identified in the laboratory.^b,c,d The equilibrium geometries of heptatriynylidene (1), cyclohepta-1,2,3,4- tetraen-6-yne (2), and heptahexaenylidene (3), which we had investigated theoretically will be discussed briefly.^e While 1 and 3 are observed in the laboratory, 2 is a hypothetical molecule. The theoretical data may be useful for the laboratory detection of 2 and astronomical detection of 2 and 3.

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FOOTNOTES:

^aTHIS WORK IS SUPPORTED BY A RESEARCH GRANT (YSS/2015/00099) FROM SERB, DST, GOVERNMENT OF INDIA.
^bApponi, A. P.; McCarthy, M. C.; Gottlieb, C. A.; Thaddeus, P. Laboratory Detection of Four New Cumulene Carbenes: H2C7, H2C8, H2C9, and D2C10, Astrophys. J. 2000, 530, 357-361.
^cBall, C. D; McCarthy, M. C.; Thaddeus, P. Cavity Ringdown Spectroscopy of the Linear Carbon Chains HC7H, HC9H, HC11H, and HC13H. J. Chem. Phys. 2000, 112, 10149-10155.
^dDua, S.; Blanksby, S. J.; Bowie, J. H. Formation of Neutral C7H2 Isomers from Four Isomeric C7H2 Radical Anion Precursors in the Gas Phase. J. Phys. Chem. A, 2000, 104, 77-85.
^eThimmakondu, V. S. The equilibrium geometries of heptatriynylidene, cyclohepta-1,2,3,4-tetraen-6-yne, and heptahexaenylidene, Comput. Theoret. Chem. 2016, 1079, 1-10.

The Center for Astrochemical Studies (CAS), at the Max Planck Institute for Extraterrestrial Physics (MPE) in Garching, has been founded to incorporate scientists with different background to elucidate the physical-chemical processes that lead to the formation of stars and planets. The CAS group includes experts in observations (including millimetre and sub-millimetre interferometry, radio and infrared telescopes), theory (physical processes and dynamics, gas-grain chemical processes and dust evolution, molecular astrophysics and collisional/rate coefficients), and laboratory. The latter is mainly focused on spectroscopic characterisation of molecular species relevant in space, including ions, radicals and astronomically complex organic molecules. In this talk the laboratory group of the CAS will be briefly presented, including current projects and planned experiments.

Methanol is one of the most abundant and important molecules in the interstellar medium, playing a key role in driving more complex organic chemistry both on grain surfaces and through gas-phase ion-molecule reactions. Methanol photolysis produces many radicals such as hydroxyl, methoxy, hydroxymethyl, and methyl that may serve as the building blocks for more complex organic chemistry in star-forming regions. The branching ratios for methanol photolysis may govern the relative abundances of many of the more complex species already detected in these environments. However, no direct, comprehensive, quantitative measurement of methanol photolysis branching ratios is available. Using a 193 nm excimer laser, the gas phase photolysis of methanol was studied in the (sub)millimeter range, where the rotational spectroscopic signatures of the photolysis products were probed. Here we present preliminary results from this experiment.

Ultraviolet spectrographs on space-borne astronomical facilities are used to study CO photochemistry primarily through observations of the A−X Fourth Positive Band System. Absorption from ¹²C¹⁶O, ¹³C¹⁶O, ¹²C¹⁸O, and ¹²C¹⁷O in diffuse interstellar clouds has been detected to date. While the necessary spectroscopic data are available to identify the isotopologues, measurements of oscillator strengths only exist for the most abundant variant, ¹²C¹⁶O. In our ongoing experiments on the DESIRS beam-line at the SOLEIL Synchrotron, we are acquiring the necessary data on oscillator strengths and term values for other isotopologues. Here we present our latest results involving A−X bands in ¹³C¹⁸O.

In the course of a recent 5 μm high-resolution infrared study of laser ablation products from carbon-sulfur targets, we have reinvestigated the ν₁ vibrational mode of the linear C₃S molecule complementing significantly the pioneering data originally reported by Takano and coworkersS. Takano, J. Tang, and S. Saito 1996, J. Mol. Spectrosc. 178, 194 In addition, located within the R-branch of the C₃S vibrational mode, a weak new band is observed which exhibits very tight line spacing. On the basis of high-level quantum-chemical calculations, this feature is attributed to the linear SC₇S species, which stands for the first gas-phase spectroscopic detection of this heavy carbon-sulfur chain.

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Footnotes:

S. Takano, J. Tang, and S. Saito 1996, J. Mol. Spectrosc. 178, 194.

Unbiased high-resolution infrared survey scans of the ablation products from carbon-sulfur targets in the 2100 to 2150 cm⁻¹ regime reveal two bands previously not observed in the gas phase. On the basis of comparison against laboratory matrix-isolation workH. Wang, J. Szczepanski, P. Brucat, and M. Vala 2005, Int. J. Quant. Chem. 102, 795nd new high-level quantum-chemical calculations these bands are attributed to the linear C₅S and SC₅S clusters. While polar C₅S was studied earlier using Fourier-transform microwave techniques,Y. Kasai, K. Obi, Y. Ohshima, Y. Hirahara, Y. Endo, K. Kawaguchi, and A. Murakami 1993, ApJ 410, L45^,V. D. Gordon, M. C. McCarthy, A. J. Apponi, and P. Thaddeus 2001, ApJS 134, 311he present work marks the first gas−phase spectroscopic detection of SC_5 V. D. Gordon, M. C. McCarthy, A. J. Apponi, and P. Thaddeus 2001, ApJS 134, 311t

The Department of Chemistry at the University of Illinois at Urbana-Champaign offers two courses in astrochemistry, one lecture (Chem 450) and one laboratory (Chem 451). Both courses present the opportunity for advanced undergraduate and graduate students to learn about various spectroscopic concepts as they are applied toward an exotic subject, astrochemistry. In the lecture course, each student devotes a substantial fraction of the course work to one of the known astromolecules, building a wiki page for it during the semester, presenting a brief oral description about it in class, and then finally writing a paper about it. The course covers electronic, vibrational, and rotational spectroscopy, along with Einstein coefficients, line widths, and the interpretation of actual astronomical spectra. It also covers relevant reactions and reaction networks. Students learn to use pgopher for modeling rotational spectra. The lab course focuses on the methylidyne radical (CH). It begins with its chemistry and spectroscopy and then moves on to laboratory study of its electronic spectrum as observed in a butane flame and then collected with the university's 12" f/15 Brashear refracting telescope in the campus observatory built in 1896. Students learn to use IGOR to reduce CCD data.

ADMIT (ALMA Data Mining Toolkit) is a Python based pipeline toolkit for the creation and analysis of new science products from ALMA data. ADMIT quickly provides users with a detailed overview of their science products, for example: line identifications, line 'cutout' cubes, moment maps, and emission type analysis (e.g., feature detection). Users can download the small ADMIT pipeline product ( < 20MB), analyze the results, then fine-tune and re-run the ADMIT pipeline (or any part thereof) on their own machines and interactively inspect the results. ADMIT has both a web browser and command line interface available for this purpose. By analyzing multiple data cubes simultaneously, data mining between many astronomical sources and line transitions are possible. Users are also able to enhance the capabilities of ADMIT by creating customized ADMIT tasks satisfying any special processing needs. We will present some of the salient features of ADMIT and example use cases.

The amount of deuterium locked up in polycyclic aromatic hydrocarbons (PAHs) has to date been an uncertain value. A near-infrared (NIR) spectroscopic survey of HII regions in the Milky Way, Large Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC), obtained with the AKARI satellite, was performed to search for features indicative of deuterated PAHs in order to better constrain the D/H ratio of PAHs. Through comparison of the observed spectra with a calculated spectrum of deuterated PAHs the aromatic and (a)symmetric aliphatic C-D stretch vibrational modes were identified. In only six out of fifty-three of the observed sources, all of which are located in the Milky Way, emission features are seen between 4.4-4.8 μm that can be unambiguously attributed to deuterated PAHs. In all cases the aromatic C-D stretching feature is weaker than the aliphatic C-D stretching feature, which indicates that deuterium addition is favored over substitution. In addition, based on the weak or absent PAD features in most of the observed spectra, it is suggested that the mechanism for PAH deuteration in the ISM is uncommon.

The majority of interstellar objects shows IR emission features also known as unidentified infrared (UIR) emission bands. These UIR bands are attributed to IR emission of highly-excited gaseous polycyclic aromatic hydrocarbons (PAHs). To understand the physical conditions and chemical evolution of the interstellar environment a precise identification of the emission carriers is desired. The 3 μm UIR feature is represented by a strong band at 3040 cm⁻¹, a plateau from 3150 to 2700 cm⁻¹ and a number of weak features within this plateau. The 3040 cm⁻¹ component is assigned to fundamental CH-stretch vibrations of PAHs, but there still remain many questions on the origin of the other features. In this work we have studied experimentally the 3 μm region of regular, hydrogenated and methylated PAHs (up to 5 rings), combining molecular beam techniques with IR-UV ion dip spectroscopy, and theoretically by density functional theory (DFT) calculations within the harmonic and anharmonic approximation. We find that (a) the 3 μm region of PAHs is dominated by Fermi resonances and thereby cannot be treated within the harmonic approximation; (b) the periphery structure of the molecules strongly affects the shape of the 3 μm band. In particular, the two-component emission interpretation can be explained by the presence of molecules with and without bay-hydrogens; (c) due to strong Fermi resonances of fundamental modes with combination bands regular PAHs can significantly contribute to the 3 μm plateau in the 3150-2950 cm⁻¹, while hydrogenated and methylated species are primarily responsible for features in the 2950-2750 cm⁻¹ region.

The idea of interstellar top down chemistry (TDC), in which molecules are produced from decomposition of larger molecules and dust in contrast to ordinary bottom up chemistry (BUC) in which molecules are produced synthetically from smaller molecules and atoms in the ISM, has been proposed in the chemistry of PAH Duley, W. W. 2006, Faraday Discuss. 133, 415^,Zhen,J., Castellanos, P., Paardekooper, D. M., Linnartz, H., Tielens, A. G. G. M. 2014, ApJL, 797, L30nd carbon chain moleculesHuang, J., Oka, T. 2015, Mol. Phys. 113, 2159^,Guzmán, V. V., Pety, J., Goicoechea, J. R., Gerin, M., Roueff, E., Gratier, P., Öberg, K. I. 2015, ApJL, 800, L33oth for diffuse^a,c and dense clouds^b,d. A simple and natural idea, it must have occurred to many people and has been in the air for sometimeL. Ziurys has sent us many papers beginning Ziurys, L. M. 2006, PNAS 103, 12274 indicating she had long been a proponent of the idea.he validity of this hypothesis is apparent for diffuse clouds in view of the observed low abundance of small molecules and its rapid decrease with molecular size on the one hand and the high column densities of large carbon molecules demonstrated by the many intense diffuse interstellar bands (DIBs) on the other. Recent identification of C₆₀⁺ as the carrier of 5 near infrared DIBs with a high column density of 2×10¹³ cm⁻² by Maier and othersCampbell, E. K., Holz, M., Maier, J. P., Gerlich, D., Walker, G. A. H., Bohlender, D, 2016, ApJ, in pressonfirms the TDC. This means that the large molecules and dust produced in the high density high temperature environment of circumstellar envelopes are sufficiently stable to survive decompositions due to stellar UV radiaiton, cosmic rays, C-shocks etc. for a long time ( ≥ 10⁷ year) of their migration to diffuse clouds and seems to disagree with the consensus in the field of interstellar grainsDraine, B. T. 2003, ARA&A, 41, 241 The stability of molecules and aggregates in the diffuse interstellar medium will be discussed.

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Footnotes:

Duley, W. W. 2006, Faraday Discuss. 133, 415\end Zhen,J., Castellanos, P., Paardekooper, D. M., Linnartz, H., Tielens, A. G. G. M. 2014, ApJL, 797, L30a\end Huang, J., Oka, T. 2015, Mol. Phys. 113, 2159 Guzmán, V. V., Pety, J., Goicoechea, J. R., Gerin, M., Roueff, E., Gratier, P., Öberg, K. I. 2015, ApJL, 800, L33b L. Ziurys has sent us many papers beginning Ziurys, L. M. 2006, PNAS 103, 12274 indicating she had long been a proponent of the idea.T Campbell, E. K., Holz, M., Maier, J. P., Gerlich, D., Walker, G. A. H., Bohlender, D, 2016, ApJ, in pressc Draine, B. T. 2003, ARA&A, 41, 241.