The CDMSShortcut: cdms.de; web address: https://cdms.astro.uni-koeln.de/. The CDMS is supported by the Verbundforschung Physik of the BMBF (German Ministry of Science and Education), project ID 05A17PK1.as founded more than 20 years ago to provide in its catalog section line lists of mostly molecular species which were or may be detected in space by radio astronomical means.H. S. P. Müller et al., Astron. Astrophys. 370 (2001) L49.he line lists are generated by fitting critically evaluated experimental data, mostly from laboratory spectroscopy, to established Hamiltonian models. The assessment of the experimental data and of the Hamiltonian model is very importante.g., C. P. Endres et al., J. Mol. Spectrosc. 327 (2016) 95.nd will be discussed in some detail. There are 1051 entries in the CDMS catalog as of end of Feb. 2021. A large fraction of the contribution will deal with recent entries and with potential laboratory needs which are often linked to Atacama Large Millimeter/submillimeter Array projects such as (R)EMoCA(Re-) Exploring Molecular Complexity with ALMA, A. Belloche et al., Astron. Astrophys. 587 (2016) A91 & 628 (2019) A10. PILSThe ALMA Protostellar Interferometric Line Survey, J. K. Jørgensen et al., Astron. Astrophys. 595 (2016) A117. and ATOMIUM.ALMA Tracing the Origins of Molecules forming dust In oxygen-rich M-type stars, L. Decin et al., Science 369 (2020) 1497.hese include numerous diatomics, frequently containing metals, with highly excited states and isotopic species for several molecules already detected in space for the last project and excited states or isotopic species of known interstellar organic molecules, but also several new ones for the other projects. Other sections of the classical CDMS include a page on Molecules in Space and a help page for users of Pickett's SPFIT/SPCAT programs. There is also a VAMDC compatible incarnation of the CDMS which is linked to a plethora of other spectroscopic, collisional, and kinetic databases via the Vitual Atomic and Molecular Data Centre portal.http://www.vamdc.org/html:<hr /><h3>Footnotes: Shortcut: cdms.de; web address: https://cdms.astro.uni-koeln.de/. The CDMS is supported by the Verbundforschung Physik of the BMBF (German Ministry of Science and Education), project ID 05A17PK1.w H. S. P. Müller et al., Astron. Astrophys. 370 (2001) L49.T e.g., C. P. Endres et al., J. Mol. Spectrosc. 327 (2016) 95.a (Re-) Exploring Molecular Complexity with ALMA, A. Belloche et al., Astron. Astrophys. 587 (2016) A91 & 628 (2019) A10., The ALMA Protostellar Interferometric Line Survey, J. K. Jørgensen et al., Astron. Astrophys. 595 (2016) A117., ALMA Tracing the Origins of Molecules forming dust In oxygen-rich M-type stars, L. Decin et al., Science 369 (2020) 1497.T http://www.vamdc.org/

Since the first molecules were detected in space, we have now reached a point where chemical and physical complexity in the interstellar medium reaches the boundaries of what human expertise and intuition alone can achieve. With every new molecule we discover, the question "What comes next?" grows more and more difficult to answer as more possibilities emerge. Conventionally, we turn to chemical models for guidance; this may be complicated when considering complex, non-LTE processes such as shocks, radiation, and grain-surface chemistry. Moreover, expansion of chemical networks typically requires hand-picked reactions and species, requiring an exhaustive knowledge of chemical and astrophysical literature, and can impose human bias on which reactions and molecules are important. As a complimentary approach to conventional chemical models, we have developed an unsupervised machine learning pipeline for predicting molecular abundances in a non-parametric fashion. Leveraging tools originally developed in high throughput drug discovery and data science, our pipeline captures and uses millions of molecules from various databases to create chemically descriptive vector representations for quantitative comparison. These representations are subsequently used to predict molecular properties in a given environment; as a proof-of-concept, we use the well-characterized chemical inventory of TMC-1, including the latest discoveries from the GOTHAM collaboration. We show that the model can be successfully conditioned on an inventory, able to reproduce column densities of unseen molecules to within an order of magnitude without any tuning parameters. Simultaneously, we are able to use the model to predict column densities of hundreds of thousands of molecules not yet detected in space, as a way to guide efforts, as well as provide a robust statistical baseline for expected abundances.

To date, many fundamental questions on the physico-chemical origin of the observed molecular complexity in space and its link to life on Earth still remain unanswered. Field work at large facilities such as free-electron lasers, synchrotrons and ion accelerators can help investigating the surface formation of biologically relevant species with unprecedented detail. During my talk, I will present recent work carried-out at FELIX Laboratory (Netherlands), ASTRID² (Denmark) and ATOMKI (Hungary) on surface molecular formation. The unique characteristics of each facility allows for the investigation of different processes occurring on interstellar and Solar System ice analogues. For instance, at FELIX Laboratory, selective IR/THz radiation spectroscopy is used to study molecular diffusion, reaction, desorption, and energy relaxation processes in ices; at ASTRID², VUV-UV-vis spectroscopy combined to 1 keV electron exposure of ices is performed in support of space missions like JUICE that are looking for traces of life-related molecules in the Solar System; and at ATOMKI, a suite of different ions and energies (200 keV - 6 MeV) are employed to bombardment space relevant ices to induce molecular synthesis in the solid phase. Results will be discussed in light of present and future observations of ice molecules in the interstellar medium and Solar System.

In radio astronomy, accurate rest frequencies of molecular transitions are indispensable for secure identification of molecular species and accurate analyses of Doppler shifts caused by motions of target sources. In observations, we have seriously realized the importance of the accurate rest frequencies of molecular transitions. For rare isotopic species lines and weak vibrational satellite lines, the situation is more serious. To overcome such a situation, an emission-type millimeter-wave spectrometer utilizing state-of-the-art radio-astronomical technologies is developed. The spectrometer is equipped with a 200 cm glass cylinder cell, a two sideband (2SB) Superconductor-Insulator-Superconductor (SIS) receiver in the 215-265 GHz band, and wide-band auto-correlation digital spectrometers. By using the four 2.5 GHz digital spectrometers, a total instantaneous bandwidth of the 2SB SIS receiver of 8 GHz can be covered with a frequency resolution of 88.5 kHz. This wide bandwidth allows us to measure relative intensities of lines which fall into the 8 GHz range. Spectroscopic measurements of HDO, CH₃CN, and CH₃OH are carried out in the 230 GHz band so as to examine frequency accuracy, stability, and sensitivity, as well as intensity calibration accuracy of our system. We confirm that the frequency accuracy for lines detected with a sufficient signal-to-noise ratio is better than 1 kHz, when the high-resolution spectrometer having a channel resolution of 17.7 kHz is used. Following this successive development of the spectrometer, we are measuring spectral lines of various isotopic species of molecules in astronomical interests.

To date,  220 individual molecular species, comprised of 19 different elements, have been detected in the interstellar and circumstellar medium by astronomical observations. In this talk, I will provide a 30,000 foot view of the demographics of this inventory, the history and lessons learned from where these molecules were first detected, and discuss interesting trends that may help guide future observations. Most importantly, I will identify critical gaps in our knowledge of this inventory, and the areas in which spectroscopic investigations in the laboratory might be most efficiently used to continue driving the ever increasing pace of molecular discovery in the ISM.

Benzonitrile (C₆H₅CN), a polar proxy for benzene (C₆H₆), has the potential to serve as a highly convenient radio probe for aromatic chemistry, provided this ring can be found in other astronomical sources beyond the molecule-rich prestellar cloud TMC-1 where it was first reported by McGuire et al. (2018). Here we present radio astronomical evidence of benzonitrile in four additional pre-stellar, and possibly protostellar, sources: Serpens 1A, Serpens 1B, Serpens 2, and MC27/L1521F. These detections establish benzonitrile is not unique to TMC-1; rather aromatic chemistry appears to be widespread throughout the earliest stages of star formation, likely persisting at least to the initial formation of a protostar. The abundance of benzonitrile far exceeds predictions from models which well reproduce the abundances of carbon chains, such as HC₇N, a cyanopolyyne with the same heavy atoms, indicating the chemistry responsible for planar carbon structures (as opposed to linear ones) in primordial sources is favorable but not well understood. The abundance of benzonitrile relative to carbon-chain molecules displays sizable variations between sources within the Taurus and Serpens clouds, implying the importance of physical conditions and initial elemental reservoirs of the clouds themselves.

As the inventory of interstellar molecules continues to grow, the gulf between small species, whose individual rotational lines can be observed with radio telescopes, and large ones, such as polycyclic aromatic hydrocarbons (PAHs) best studied in bulk via infrared and optical observations, is slowly being bridged. Understanding the connection between these two molecular reservoirs is critical to probing topics such as the interstellar carbon cycle, but will require pushing the boundaries of how far we can probe molecular complexity while still retaining observational specificity. Toward this end, we have developed a method for detecting and characterizing new molecular species in single-dish observations toward sources with sparse line spectra. Application of this method to data from the ongoing GOTHAM (GBT Observations of TMC-1: Hunting Aromatic Molecules) Green Bank Telescope (GBT) large program has resulted in ten new interstellar species detections thus far. In this talk, I present an overview of the method and demonstrate that it is a robust detection technique, highlighting both its strengths and limitations.

In order to unveil how chemistry complexity build up in space, Complex Organic Molecules (COMs) are receiving more and more attention from the astrochemical and astrobiological community. Nowadays, especially after the glycine detection in the 67P/C-G comet, there is a strong interest to detect amino acids and their precursors in space, with the aim of gaining understanding in their formation process. The most promising pathways to the synthesis of amino acids, namely photochemically and through the Strecker synthesis, include in their final step the hydrogenation of an aminonitrile molecule. It's in this context that the importance of 3-amino-2-propenitrile (APN) makes its appearance. This aminonitrile is simply obtained in gas phase or in solution by mixing cyanoacetylene (HCCCN) and ammonia (NH₃), both largely present in the Universe. Therefore, starting from previous work taken as reference, the APN spectrum has herein collected and characterised using the MPE's CASAC (Center of Astrochemical studies Absorption Cell). Here the frequency modulated signal of synthesiser, locked to a Rb atomic clock, is multiplied several times to cover a possible frequency range from 40 GHz to 1.6 THz. The interaction of the radiation source with the molecular sample is hence acquired by a InSb hot electron bolometer detector, and demodulated by a lock-in amplifier. The unprecedented level of detail in the data has therefore allowed the characterisation of the rotation and distortion constants of the APN at a deeper standard, providing a new level of precision for the hunt of this molecule in space with the highest level of confidence since now.

Hydrogen cyanide (HCN) is ubiquitous in the interstellar medium, especially in the dying carbon star IRC+10216, where its abundance and reactivity are of great astrophysical relevance. We have developed a safe, robust synthesis and storage procedure for pure HCN gas, which is necessary for carrying out further studies on the reactivity of HCN in the gas phase. We present the high-resolution, rotationally-resolved vibrational spectrum of gaseous HCN obtained with a Nicolet iS50 Fourier transform IR (FTIR) spectrometer. Line-by-line frequency and spectral intensity data from the HITRAN database were used to fit the experimental FTIR spectra for the ν₃ ro-vibrational transition (C-H stretch at 3300 cm⁻¹) of HCN. We will describe the current state of knowledge for this transition and compare our findings with the HITRAN database.

Out of the more than 200 individual molecular species already identified in the ISM, nearly 16% of the molecules contain a cyano functional group (see www.astro.uni-koeln.de/cdms/molecules). An interesting extension to this is studying molecules that contain an additional functional group. We present a comprehensive study on methyl cyanoacetate (MCA) whose condensed formula is NCCH₂COOCH₃. It is a molecule whose two functional groups (cyano, -CN, and ester, -COOCH₃) have already been identified individually in the ISM. The rotational spectrum of MCA was obtained in the frequency range of 2-26 GHz using two chirped-pulse Fourier transform microwave (CP-FTMW) spectrometers, namely the COMPACT spectrometer and the 18-26 GHz spectrometer. The ¹⁴N nucleus (I=1) in the cyano group, is responsible for the observation of the nuclear quadrupole hyperfine splitting (HFS) of rotational transitions. The ester functional group contains a methyl top that rotates with respect to the molecular frame and couples with the overall rotation (computed barrier height for internal rotation, V₃ is 309 cm⁻¹), giving rise to further splitting of each transition into A and E states. Both the nuclear quadrupole HFS and the methyl internal rotation splitting were resolved, and it was possible to obtain a single fit for all the rotational parameters using the XIAM program.¹ This study of MCA in the 2-26 GHz region would provide insights into how the barrier height is affected by the presence of electron-withdrawing/donating moieties attached to the ester group. For example, in methyl carbamate,² V₃ is 352 cm⁻¹, while in methyl acetate,³ V₃ is 425 cm⁻¹. Furthermore, the experimental data obtained from this study can facilitate searches for this molecule with various radio observatories, for example, the Jansky Very Large Array (JVLA) and the Radio Telescope Effelsberg. (1) H.Hartwig and H.Dreizler, Z. Naturforsch 51a, 923-932 (1996) (2) J. Sheridan et al. J. Mol. Spectrosc. 80, 1-11 (1980) (3) B. Bakri et al. J. Mol. Spectrosc. 215, 312–316 (2002)

SO is an important radical found in many astronomical sources such as the atmosphere of Io and the atmosphere of Venus. In order to create more complete line lists, we fit spectroscopic data on SO from the literature using PGOPHER. The fits covered v=0 to v=6 for the X³Σ⁻ state, v=0-5 for the a¹∆ state and v=0-2 for b¹Σ⁺ state. The B_v and G_v polynomial coefficients for each state were input into LeRoy’s RKR program to produce pointwise potential energy curves. High level ab initio calculations, including spin-orbit coupling, were carried out to obtain the electric transition dipole moment functions for the nominally forbidden b¹Σ⁺− X³Σ⁻ and a¹∆− X³Σ⁻ transitions. The RKR potentials and transition dipole moment points were input into LeRoy’s LEVEL program to calculate the transition dipole matrix elements for all possible b-X and a-X bands. For the b¹Σ⁺− X³Σ⁻ transition, the electric and magnetic transition dipole matrix elements were scaled using the experimental values of μ₀ = 0.0107 D, μ₁ = -0.0119 D and M = 0.16 μ_B obtained by Setzer et al.K.D. Setzer, E.H. Fink, and D.A. Ramsay, High-resolution Fourier transform study of the b¹Σ⁺− X³Σ⁻ and a¹∆− X³Σ⁻ transitions of SO, J. Mol. Spectrosc. 198, 163-174 (1999).or the 0-0 band. The transition dipole moment matrix elements were used in PGOPHER to produce our line lists for the b¹Σ⁺− X³Σ⁻ and a¹∆− X³Σ⁻ transitions.

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Footnotes:

K.D. Setzer, E.H. Fink, and D.A. Ramsay, High-resolution Fourier transform study of the b¹Σ⁺− X³Σ⁻ and a¹∆− X³Σ⁻ transitions of SO, J. Mol. Spectrosc. 198, 163-174 (1999).f

The e-PYTHEAS project combines theoretical and experimental work with exoplanet modelling applications. Our approach is to use theoretical research validated by laboratory experiments and to then inject it into models of the atmospheres of the giant gaseous planets in the solar system and other planetary systems. Our consortium of five French laboratories and associated partners proposes to improve the existing high-temperature spectroscopy data for several molecular species detected in exoplanets. More in detail, the goals are to: (1) Generate experimental and synthetic spectra in the 1-17 μm wavelength region for hydrocarbons and their isotopologues such as ¹²CH₄, ¹³CH₄, CH₃D, C₂H₂, C₂H₄ and C₂H₆ up to 2500 K. (2) Produce complete line lists without the current limitations in frequency and temperature ranges. (3) Record new absorption and emission spectra at high temperature by unique techniques developed by IPR, LIPhy and GSMA. (4) Produce global ab initio spectra predictions. (5) Validate and empirically correct them using spectra measurements. (6) Use the generated spectroscopic data to enhance the output of radiative transfer codes and improve our understanding of the processes involved in hot gaseous environments thanks to the analysis of a large amount of observations. (7) Determine the role of the target species on the thermal structure of hot exoplanets and hence to a new understanding of the origin and evolution of exoplanetary atmospheres. The results will help to analyze data and address essential questions on the formation and evolution of planetary systems, such as retrieved by ESA's M4 space mission ARIEL in 2029. See the project's website: http://e-pytheas.cnrs.fr