Ethyl cyanide (CH₃CH₂CN) is a well-known constituent of interstellar clouds and has recently been detected in the atmosphere of Titan.Cordiner, M. A., Palmer, M. Y., Nixon, C. A. et al. 2015, ApJL, 800, L14.t is so abundant in some interstellar clouds that its doubly substituted carbon-13 isotopologues, as well as highly excited vibrational satellites have been detected there.Margulès, L., Belloche, A., Müller, H. S. P. et al. 2016, A&A, 590, A93 and references therein.ecause of the high abundance and high proton affinity of CH₃CH₂CN, protonated ethyl cyanide (CH₃CH₂CNH⁺) is a plausible intermediate in the chemistry of interstellar clouds and planetary atmospheres. Here we report the detection of CH₃CH₂CNH⁺ by Fourier transform microwave spectroscopy of a supersonic molecular beam. Thirteen a-type rotational transitions have been observed between 8 and 44 GHz, some with partially resolved nitrogen hyperfine structure. This data set allows determination of all three rotational constants, as well as several of the leading centrifugal distortion constants to high accuracy. The derived rotational constants and those calculated at the CCSD(T) level of theory agree to better than 0.2%. Nitrogen hyperfine structure in the lower rotational transitions is so compact that only the quadrupole coupling tensor element along the a-inertial axis (χ_aa) could be determined. With accurate laboratory data in hand, a radio astronomical search for CH₃CH₂CNH⁺ in publicly available spectral line surveys as well as through dedicated observations can now be undertaken with high confidence. Cordiner, M. A., Palmer, M. Y., Nixon, C. A. et al. 2015, ApJL, 800, L14.I Margulès, L., Belloche, A., Müller, H. S. P. et al. 2016, A&A, 590, A93 and references therein.B

Understanding how, when, and where complex organic and potentially prebiotic molecules are formed is a fundamental goal of astrophysics and astrochemistry and an integral part of origins-of-life studies. The recent images from the Atacama Large Millimeter/submillimeter Array (ALMA) of a potentially planet-forming disk around a young star with an age of only 0.5-1 Myr (million years) have highlighted the importance of the physics and chemistry of the early protostellar stages. A particular focus of ALMA observations is the search for complex molecules in regions of high- and low-mass star formation. Methanol is among the most abundant molecules in star-forming regions, to such an extent that it is considered as an interstellar "weed". Thus, its numerous isotopologues must be accounted for in search for new complex molecules as yet unknown. Here, Calculatus Eliminatus approach – "… can help an awful lot. The way to find a missing something is to find out where it's not!" The Cat in the Hat (Video), Dr. Seuss. In other words, if we establish all the knowns, then we can focus on the remaining unknowns.This talk will report progress in our current effort in our on−going journey to pursue the weeding of the cosmos, focusing on CH_3OD and ^13CH_3OD. While CH_3OD is of great interest to a considerable fraction of the radio astronomical community, the significance of ^13CH_3OD originates from Protostellar Interferometric Line Survey (PILS) J. K. Jørgensen et al., Astron. Astrophys. 595 (216) 117. of the low-mass protostars IRAS 16291-2422 with ALMA. Here, many lines of CH₃OH, ¹³CH₃OH and even CH₂DOH are optically thick, so that the ratio of CH₃OD to ¹³CH₃OD may serve as a valuable probe of the ¹²C/¹³C ratio of methanol. New laboratory measurements obtained at Universität zu Köln will be described for: (i) sample mixture of ¹³CH₃OH and CH₃OD yielding enriched ¹³CH₃OD features from approximately 134 GHz to 510 GHz and (ii) CH₃OD from approximately 154 GHz to 510 GHz and from 1.12 THz to 1.34 THz.

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The Cat in the Hat (Video), Dr. Seuss.\end J. K. Jørgensen et al., Astron. Astrophys. 595 (216) 117.

Ethanimine and cyanomethanimine are possible precursors of amino acids, and thus they are considered important prebiotic molecules that may play an important roles in the formation of biological building blocks in the interstellar medium. In addition, their identification in Titan's atmosphere would be important for understanding the abiotic synthesis of organic species. For both molecules, an accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers has been carried out by means of a composite scheme based on coupled-cluster techniques. By combining the computational results with new millimeter-wave measurements, up to 300 GHz for ethanimine and to 420 GHz for cyanomethanimine, the rotational spectra of both isomers can be accurately predicted up to 500 GHz for ethanimine and 700 GHz for cyanomenthanimine. For the latter, spectral features have been searched in the mm-wave range using the high-sensitivity and unbiased spectral surveys obtained with the IRAM 30-m antenna in the ASAI context, thus sampling the earliest stages of star formation from starless to evolved Class I objects.

A fundamental question in the field of astrochemistry is whether the molecules essential to life originated in the interstellar medium and, if so, how they were formed. Nitrogen-containing heterocycles are of particular interest because of their role in biology. The discoveries of these molecules on meteorites provide evidence to support an interstellar origin. Yet, while many N-containing species have been identified in the interstellar medium, N-heterocycles have not, perhaps due to their susceptibility to UV photolysis. Recently, the β-cyanovinyl radical () was implicated in the low temperature formation of N-heterocycles. While neutral vinyl cyanide () has been rotationally characterized and detected in the interstellar medium, has not. In order to understand how this radical contributes to interstellar chemistry, further study is needed. We have launched a search for the rotational spectrum of HCCHCN using both cavity and broadband FTMW spectrometers, the current status of which will be discussed in this talk. Rotational characterization of this radical will enable a search in the interstellar medium and further experimental work on the low temperature formation of N-heterocycles.

The partially deuterated isotopologues of H₃⁺ have proven to be valuable probes of interstellar environments. In low temperature regions ( < 20 K) such as dark molecular clouds, deuterium fractionation leads the ratios of D₂H⁺/H₃⁺ and H₂D⁺/H₃⁺ to be orders of magnitude greater than that of HD/H₂.H. Roberts, E. Herbst, and T. J. Millar, Astrophys. J., 591, L41 (2003). nlike H₃⁺, D₂H⁺ and H₂D⁺ have permanent dipole moments and their allowed rotational transitions can be used to probe interstellar conditions and give an indirect method of detection for H₃⁺. There are still unobserved transitions of D₂H⁺ that are within the coverage of observatories such as the Stratospheric Observatory for Infrared Astronomy (SOFIA) which have relatively large uncertainties (8-16 MHz). Recently, we have measured over 20 rovibrational transitions of D₂H⁺ with MHz-level uncertainty using the technique Noise-Immune Cavity-Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS).J. N. Hodges, A. J. Perry, P. A. Jenkins II, B. M. Siller, and B. J. McCall, J. Chem. Phys, 139, 164201 (2013).hese new measurements can be used to improve predicted frequencies of pure rotational transitions using combination differences and an improved fit to an effective Hamiltonian.

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H. Roberts, E. Herbst, and T. J. Millar, Astrophys. J., 591, L41 (2003). U J. N. Hodges, A. J. Perry, P. A. Jenkins II, B. M. Siller, and B. J. McCall, J. Chem. Phys, 139, 164201 (2013).T

Astrophysical observations of radioactive isotopes, like ²⁶Al, ⁴⁴Ti, or ⁶⁰Fe, provide insight into the nucleosynthesis of stellar cores. The detection of characteristic γ-photons, which are released during radioactive decay, is used to map their spatial distribution on large scale. In general, the assignment to certain stellar objects fails due to limited sensitivity.
An alternative approach is the observation of molecules containing radioactive isotopes. Radio-telescope facilities, like ALMA, can identify these species via their rotational transitions. In the outer atmosphere of late-type stars, the molecular condensation starts with simple diatomic particles containing oxides of refractory elements. The astrophysical detection of diatomic radioactive molecules requires highly accurate rotational transition frequencies, which can be obtained from laboratory measurements of stable isotopologues using mass-independent Dunham parameters.
In this work, systematic studies are presented for ²⁶AlO, ⁴⁴TiO, and ⁶⁰FeO, as most promising tracers of nucleosynthesis in stellar environments, based on high-resolution measurements on the rotational transitions of their abundant stable isotopologues. Experiments were performed when a solid target (Al, Ti, Fe) is evaporated by a pulsed laser into an oxygen-rich buffer gas to form simple metal oxides. An adiabatically planar expansion of the gas into a vacuum chamber cools the gas to a few tens of Kelvin and subsequently, Doppler-free rotational absorption spectra are recorded in the frequency range up to 400 GHz. A global data analysis, which also includes results from the literature, reveals the molecular structure beyond the Born-Oppenheimer (BO) limit, resulting in experimentally derived BO correction coefficients of these species for the first time. Based on this analysis, the rotational transitions of the radioactive molecules are determined with high accuracy at the sub-MHz level, which enables their unambiguous identification in stellar environments.

The pure rotational spectrum of the AlC₂ radical (~X²A₁) has been recorded for the first time using Fourier transform microwave/millimeter-wave (FTMmmW) techniques in the frequency range 21 – 65 GHz. AlC₂ was produced in a supersonic jet from the reaction of aluminum, generated by laser ablation, with a mixture of CH₄ or HCCH, diluted in argon, with a DC discharge. Three transitions (N_Ka,Kc = 1₀₁ → 0₀₀, 2₀₂ → 1₀₁, and 3₀₃ → 2₀₂) were measured, consisting of multiple fine/hyperfine components, resulting from the unpaired electron and the aluminum-27 nuclear spin (I = 5/2). The data were analyzed using an asymmetric top Hamiltonian and rotational, fine structure, and hyperfine constants were established. These results are in excellent agreement with previous theoretical calculations and optical spectra. An r₀ structure of AlC₂ was determined to be r(Al–C) = 1.924 Å, r(C–C) = 1.260 Å, and θ(C–Al–C) = 38.2^°. The data are consistent with a T-shaped geometry with Al⁺C₂⁻ bonding. A search for AlC₂ in the circumstellar envelope of IRC+10216 is currently underway.

Polycyclic aromatic hydrocarbons (PAHs) are believed to act as catalysts in ice grains formation. The formation of interstellar ice can thus be described as an aggregation process of gaseous water starting on PAH surfaces. The structural investigation of PAH-H₂O clusters, therefore, represents a first and important step to undertake in order to shed light on potential ice grains formation pathways. Previous studies have focused on mimicking the initial stage of this aggregation process in laboratories by forming complexes between PAH and water molecules in the gas phase and investigating them by microwave spectroscopy. As the outcome of these studies, precise information on the structure and intermolecular interactions were obtained [1,2]. Herein we take this approach further and present preliminary data on the structural investigation of the complex of phenanthrene, a PAH molecule featuring three fused benzene rings, and water. Its pure rotational spectrum was recorded using a chirped pulse Fourier transform microwave spectrometer (CP-FTMW) operating in the region 2-8 GHz, and structural information on the respective water clusters can be obtained.
[1] Pérez, C.; Steber, A. L.; Rijs, A. M.; Temelso, B.; Shields, G. C.; Lopez, J. C.; Kisiel, Z.; Schnell, M., Phys. Chem. Chem. Phys. 2017, 19, 14214-14223. [2] Steber, A. L.; Pérez, C.; Temelso, B.; Shields, G. C.; Rijs, A. M.; Pate, B. H.; Kisiel, Z.; Schnell, J. Phys. Chem. Lett. 2017, 8, 5744-5750.

The elusive C-H vibration-rotation transitions of the fundamental ions ¹²CH⁺ and ¹³CH⁺ have been observed for the first time in the laboratory. The technique of state-dependent attachment of He atoms to these ions in a cryogenic trapO. Asvany, S. Brünken, L. Kluge, and S. Schlemmer 2014, Appl. Phys. B, 114, 203-211.as been used to obtain high-resolution rovibrational data. The excitation source is an IR OPO whose frequency is measured using a frequency comb. In addition, the lowest frequency rotational transitions of ¹²CH⁺, ¹³CH⁺ and ¹²CD⁺ have been revisitedS. Yu, B. J. Drouin, J. C. Pearson and T. Amano 2015, in Contribution RD06, 70th International Symposium on Molecular Spectroscopy.^,T. Amano 2010, Astrophys. J. Lett., 716, L1.^,S. Brünken, L. Kluge, A. Stoffels, J. Pérez-Ríos, and S. Schlemmer 2017, J. Mol. Spec. 332, 67.sing a synthesizer and a multiplier chain with the same ion trap, leading to a significant improvement of their rest frequency values.

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O. Asvany, S. Brünken, L. Kluge, and S. Schlemmer 2014, Appl. Phys. B, 114, 203-211.h S. Yu, B. J. Drouin, J. C. Pearson and T. Amano 2015, in Contribution RD06, 70th International Symposium on Molecular Spectroscopy.\end T. Amano 2010, Astrophys. J. Lett., 716, L1. S. Brünken, L. Kluge, A. Stoffels, J. Pérez-Ríos, and S. Schlemmer 2017, J. Mol. Spec. 332, 67.u

Cyclopropenylidene (c-C₃H₂) is one of the few polyatomic hydrocarbons ubiquitous in our galaxy, despite its reactive carbene nature (see e.g. [1]). Because it is so widely distributed in space, and because its ¹³C, D, and D₂ isotopologues have also been detected (see e.g. [2]), c-C₃H₂ is an ideal probe of the physical conditions in various astrophysical objects. It is surprising though that its vibrational satellites have yet to be detected in the interstellar medium. To enable the interstellar detection of vibrationally excited c-C₃H₂, and observe for the first time the elusive ν₄ and ν₉ vibrational modes, we have undertaken an extensive investigation of its spectrum from the centimeter to the submillimeter wavelengths, resulting in the observation of many new vibrational satellites in a promising spectral region for astronomical observations. Our measurements are supported by anharmonic rovibrational calculations using a high-quality ab initio potential energy surface, with particular attention paid to the ν₄/ν₉ Coriolis interaction.
[1] S. Spezzano et al., The Astrophysical Journal Supplement Series 200, 1 (2012) [2] S. Spezzano et al., The Astrophysical Journal Letters, 769, L19 (2013)

There are to date about 200 molecules that have been detected in the interstellar medium or circumstellar shells. Among these molecules, several tens are the methylated derivatives of compounds previously detected. For several years, we have been studying molecules belonging to the imine family. Following the detection of the dimer of HCN, the cynaoethanimine, its methylated derivative, methylimino-acetonitrile appears as a privileged target. Methylimino-acetonitrile has two isomers E and Z. According to quantum chemical calculations, the E isomer is more stable than Z by about 1.5 kJ/mol. There was no spectrosocpic data allowing detection without ambiguity of this molecule in the interstellar medium. We recorded and analyzed the spectra of methylimino-acetonitrile up to 660 GHz. This compound is not stable in laboratory conditions, it was produced in-situ by pyrolisis and introduced in a 1 m long pyrex cell in a flow mode. The E isomer represents an interesting case from spectroscopic point of view. Even if the barrier to internal rotation of the methyl top is quite high 714 cm⁻¹, some A-E tunneling splittings were observed. This is due to quite high ρ value: 0.274, just slightly smaller than the acetaldehyde value of 0.329. The analysis is performed using the RAM36 codeIlyushin, V.V. et al; J. Mol. Spectrosc. 259, (2010) 26 The spectroscopic results will be presented.

Acknowledgements: These results were supported by the Programme National PCMI of CNRS/INSU with INC/INP co- funded by CEA and CNES, the French National Research Agency (ANR-13-BS05-0008 ”IMOLABS”

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Ilyushin, V.V. et al; J. Mol. Spectrosc. 259, (2010) 26.