The project of Lille Spectroscopic Database (https://lsd.univ-lille.fr) emerged from a large number of molecules of astrophysical and atmospheric interest exhibiting large amplitude motions studied in PhLAM laboratory in the last decade. To fit their spectra and to calculate spectral predictions we used many different codes including SPFIT/SPCAT program suite. While the latter is the main fitting/predicting tool for widely known CDMS and JPL databases, spectral predictions obtained with other codes are somehow scattered in the supplementary data of publications and are eventually available in the another well known Splatalogue database. For this reason, we decided to develop and maintain the Lille Spectroscopic Database which will contain the spectral predictions of the molecules studied by our group in Lille. The new database will provide a typical functionality of other databases: predictions will be available in different formats including different intensity units, and at different temperatures; a search within the full database will be possible to limit the predictions for a particular range of frequencies, intensities or quantum numbers. We will also provide and present an application programming interface (API) that allows the integration of our database into other software. We thank the Mésocentre de Calcul Scientifique Intensif de l'Université de Lille for hosting the database.

At a distance of 1.3 kpc, NGC 6334I is one of the nearest massive star-forming regions. Previous studies of the source have revealed a number of prodigious hot cores, each of which exhibit a rich molecular inventory. Our previous work on NGC 6334I examined spectra from a limited number of positions scattered throughout the source in order to sample the various physical conditions that can be found. In an effort to better characterize the underlying complex physical and chemical structure of this massive star-forming cluster we have conducted an automated LTE fit of the emission spectra corresponding to each of over 8000 pixels surrounding the hot cores using two ALMA Band 7 tunings with a resolution of 0.26” (340 AU). For each pixel we derive an excitation temperature as well as the column density for each of the 25 most prominent molecular species. Spatial maps of the derived properties for the molecules will be presented with a particular focus on the three C₂H₄O₂ isomers and how the clustered star formation appears to impact their abundances. These molecular properties will be discussed within the context of the physical structure of the protocluster.

Accurate reference laboratory data represents a key element for understanding any remote observations in particular astrophysical surveys. The subject has grown in importance with the recent discovery of the capability to observe spectra of exoplanets or the ability to closely probe space objects like in the case of the Rosetta mission. This need is even timelier with the James Webb telescope being deployed for operation and the new space missions dedicated to the exoplanetary spectroscopic studies like Twinkle, and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) destined to be launched in 2024 and 2029, respectively. The current contribution is an overview of our work concerning the acquisition of such accurate reference data in the case of ammonia molecule based on the combination of room temperature Fourier transform spectra (both old and new), tunable laser spectroscopy in cooled Herriott cell, and in a supersonic expansion. In addition, multiple new techniques to improve the whole process of spectra analysis were used, mainly: the enhanced multi-temperature treatment for determination of empirical lower state energies, intensity-based combination differences process for determination of quantum assignments, or the accurate referenced frequency calibration to verify the absolute line positions with a sub 0.001 cm⁻¹ accuracy.

When I read Townes and Schawlow's textbook as a beginning student, I was puzzled by the symmetric top selection rule ∆K = 0, because this rule corresponds to cylindrical symmetry C_∞; applying it to NH₃ with C₃ symmetry cannot be right. At that time, however, I did not pursue how this wrong rule affect the actual spectrum. 10 years later interstellar NH₃ was discovered by Townes’ group. When I read the discoverers’ claim that lifetimes of (J, K) = (2,2) and (3,3) metastable levels are “longer than the lifetime of the Universe”, it was obvious that this wrong statement resulted from the wrong ∆K = 0 selection rule. Accurate theoryT. Oka, F.O. Shimiza, T. Shimizu, J.K.G. Watson, ApJ 165, L15 (1971)ave the life times of the (2,2) and (3,3) metastable levels to be 230 years and 44 years, respectively, 10⁸ times shorter than the lifetime of the Universe. The theory also predicted ∆k = ±3 pure rotational transitions which were observed for PH₃, PD₃ and AsH₃F.Y. Chu, T. Oka, J. Chem. Phys. 60, 4612 (1974)In this paperT. Oka, J. Mol. Spectrosc. 379, 111482 (2021) calculate spontaneous emission via forbidden transitions for astrophysically important symmetric tops; oblate tops NH_3, H_3O^+, H_3^+, and prolate tops CH_3 T. Oka, J. Mol. Spectrosc. 379, 111482 (2021)I

The detection of the fullerenes C₆₀ and C₇₀ in the interstellar medium (ISM) has transformed our understanding of chemical complexity in space, and have also raised the possibility for the presence of even larger molecules in astrophysical environments. Here we report in situ heating of analog silicon carbide (SiC) presolar grains using transmission electron microscopy (TEM). These heating experiments are designed to simulate shocks occurring in post-AGB stellar envelopes. Our experimental findings reveal that heating the analog SiC grains yields hemispherical C₆₀-sized nanostructures, which later transform into multi-walled carbon nanotubes (MWCNTs). These MWCNTs are larger than any of the currently- observed interstellar fullerene species, both in overall size and number of C atoms. These experimental results suggest that such MWCNTs are likely to form in post-AGB shocks, where the structures, along with the smaller fullerenes, are subsequently injected into the ISM.

While it is now well established that the interstellar medium (ISM) is characterized by a rich and complex chemistry, we are far from a complete census of the interstellar molecules and the understanding about how they form and evolve is at a primitive stage. Concerning the former issue, a significant number of features in radioastronomical spectra are still unassigned. To fill this gap, a huge laboratory effort is required, which is increasingly based on integrated experimental and computational strategies. This contribution aims to present examples of an integrated rotational spectroscopy - quantum chemistry approach for supporting radioastronomical observations. In this respect, a significant example is provided by the recent characterization of (Z)-1,2 ethenediol, a key prebiotic intermediate in the formose reaction Melosso et al. Chem. Commun. 58, 2750 (2022)

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Footnotes:

Melosso et al. Chem. Commun. 58, 2750 (2022).

At the centimeter wavelength, the single-dish observation has suggested that the Sgr B2 molecular cloud at the Galatic center hosts weak maser emission from complex molecules, including CH₂NH, HNCNH, and HCOOCH₃ (McGuire et al., 2012; Faure et al., 2014, 2018). Because molecular masers often trace specific conditions within the massive star-forming regions, finding new maser transitions and species provides critical insights into the physical structures hidden behind the thick dust. However, the lack of distribution information of these new maser species had prevented us from not only quantitatively assessing the observed spectral profiles but also constraining their pumping mechanisms. In this talk, we present a rigorous mapping study toward the galactic center to resolve the region where the complex maser emission originates. By comparing the distribution of several maser emissions, it is revealed that the new maser species have a close spatial relationship with the CH₃OH Class I masers. This relationship serves as observational evidence to suggest a similar collisional pumping mechanism for these maser transitions.

Astrophysical molecular spectroscopy is an important method of searching for new physics through probing the variation of the proton-to-electron mass ratio, μ, with existing constraints limiting variation to a fractional change of less than 10⁻¹⁷/year. To improve on this constraint and therefore provide better guidance to theories of new physics, new molecular probes will be useful. These molecular probes must have spectral transitions that are observable astrophysically and have different sensitivities to variation in the proton-to-electron mass ratio. This talk will focus on the development of a high-throughput methodology to calculate the sensitivities of transitions in diatomic and polyatomic molecules with established spectroscopic models. The calculations required are straightforward; reproducing the line list with a slight increase in nuclear masses and comparing the original and mass-shifted energies and transition frequencies. The major challenge was in matching the quantum states in the original and mass-shifted data as the quantum number descriptions were not always preserved when the state was heavily mixed - unfortunately precisely those states likely to have high sensitivities to μ variation. These challenges were far more severe in polyatomics than diatomics. Our results found that even a conservative intensity cut-off of 10⁻³⁰ cm/molecule at 100 K (astrophysically relevant interstellar conditions) removed almost all transitions with high sensitivity to μ variation. There were no new clear transitions of interest were identified in the 22 diatomic and 5 polyatomic molecules investigated, with the low-frequency diatomic parity changing and polyatomic inversion transitions having the strongest sensitivities. In the diatomics we investigated, high sensitivity was observed in low-frequency rovibronic transitions arising from accidental near-degeneracy between electronic states were observed, but these have very low intensity (as the states involved were high in energy) and thus not likely to be observable astrophysically. This insight allows screening of diatomics without spectroscopic models for sensitivity to μ variation; we conclude that no diatomic known extragalactically is likely to have transitions with high sensitivity to μ variation.

Diamondoids are a class of stable, aliphatic molecules arranged in cage-like structures and serve as a link between small, cyclic hydrocarbons and bulk nanodiamonds. Similarities have been observed between the infrared spectra of diamondoids and unidentified infrared emission bands seen in the spectra of young stars with circumstellar disks.¹ It is also suggested that the radical cations of these molecules could contribute to features in the well-known but largely unassigned diffuse interstellar bands due to their low ionization energy and absorption in the visible range.² However, only the optical spectrum of the adamantane cation has been measured so far.³ Herein, we report the first optical spectrum of the diamantane radical cation (C₁₄H₂₀⁺) between 400 and 1000 nm in the gas phase. Measurements were taken in a tandem mass spectrometer by photodissociation of mass-selected ions cooled in a cryogenic 22-pole ion trap held at 5 K. The optical spectrum reveals two broad and unresolved bands centered near 760 and 450 nm that are assigned to the D₂(²E_u) ← D₀(²A_1g) and D₅(²A_2u) ← D₀(²A_1g) transitions using time-dependent density function theory calculations. These calculations also assist to explain the lack of vibrational structure as the result of lifetime broadening and Franck-Condon congestion arising from large geometry changes.
Literature:
¹O. Pirali, M. Vervloet, J. E. Dahl, R. M. K. Carlson, A. G. G. M. Tielens, J. Oomens, Astrophys. J., 661, 919–925 (2007).
²M. Steglich, F. Huisken, J. E. Dahl, R. M. K. Carlson, T. Henning, Astrophys. J., 729, 91–100 (2011).
³P. B. Crandall, D. Müller, J. Leroux, M. Förstel and O. Dopfer, 2020, Astrophys. J. Letters, 900, L20

We reexamine the abundance of CS in diffuse molecular clouds from lines in the C-X (0, 0) band by including additional sight lines not available in previous work and by extracting information on molecular structure. The analysis incorporates results from our recent large-scale calculations on CS photodissociation and adopts the approach taken in our study of the F-X (0, 0) and (1, 0) bands in C₂. Syntheses of the high-resolution spectra with the best signal to noise yielded wavelengths for the R(0), R(1), and P(1) lines and their widths. Significant line broadening is seen, yielding a predissociation width of 23.7±0.7 mÅ; this value is within a factor of 2 of the predictions from the calculations. The computations also revealed similar rotational constants for the X and C states. The differences in transition frequencies among the three lines then suggest that the P(1) line is shifted by 2.27 cm⁻¹. We also found evidence that the strengths for the R(1) and P(1) lines were affected by the perturbation. The fits to the data for the other directions in the sample adopted these refined line parameters to determine column densities. A comparison of the CS column densities with results for CH, CN, CO, and H₂ helped inform us of the chemical pathways leading to CS in diffuse molecular gas.

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous in space and most astronomical spectra, from the interstellar medium (ISM) to distant galaxies, including regions of massive star formation, the general ISM, and star forming spiral galaxies out to red-shifts of z>4, are dominated by their ubiquitous infrared emission features. Whether the PAH bands are intimately associated with the object, or foreground/background confounding features, they will have to be understood, separated from other features in the spectra, and analyzed for the information they contain on the physical and chemical properties of their surrounding environments. High-resolution laboratory spectra of PAHs measured in an astrophysically-relevant environment are critical to answer these questions. The most challenging task is to reproduce, as closely as technically possible, the physical and chemical conditions that are present in space (i.e., cold gas phase molecules and ions, isolated in a collision-free environment). Comparable conditions can be achieved using the cosmic simulation chamber (COSmIC) developed at NASA Ames. COSmIC allows to measure gas phase spectra of neutral and ionized interstellar PAH analogs by associating a free supersonic jet with a soft ionizing discharge that generates a cold plasma expansion (100 K). Using the Cavity Ring Down Spectroscopy (CRDS) technique, rovibronic absorption spectra of PAHs and PAH derivatives seeded in Ar supersonic jet expansions are measured in the NUV-Vis-NIR region. The resulting spectra provide a critical tool to identify and characterize specific molecules and ions in astrophysical environments. We intend to expand the capabilities of our current CRDS system to the NIR and MIR up to 3.5 um in order to provide accurate high-resolution laboratory spectra that will help validate the extensive NASA Ames’ PAH database and will greatly benefit the interpretation of future James Webb Space Telescope NIRSpec observational data.

The interplay of the chemistry and physics that exists within astrochemically relevant sources can only be fully appreciated if we can gain a holistic understanding of their chemical inventories. Previous work by Lee et al. demonstrated the capabilities of simple regression models to reproduce the abundances of the chemical inventory of TMC-1, as well as provide predictions for the abundances of new candidate molecules. It remains to be seen, however, to what degree TMC-1 is a “unicorn” in astrochemistry, where the simplicity of its chemistry and physics readily facilitates characterization with simple machine learning models. Here we present an extension in chemical and physical complexity to an extensively studied hot star forming region, Orion-KL. Unlike TMC-1, the Orion-KL nebula is composed of several structurally distinct environments that differ chemically and kinematically, wherein abundances of molecules between components can have non-linear correlations that can cause the unexpected appearance or even the lack of unlikely species in various environments. A proof-of-concept study was performed to assess if similar regression models could accurately reproduce the abundances from the XCLASS chemical inventory obtained by the Herschel spectral survey. A new self-referencing embedded string (SELFIES) molecular embedder was adopted to account for vibrationally excited states and isotopologues. This additional complexity is considered with a hierarchical classification algorithm to indicate any relationships between environments with respect to the present species. Alongside the promising performance of our regression and classifier models, we attempted to fully capture the complexity of Orion-KL with increased efficiency using a neural network. The results of the classical models and neural network, as well as a discussion of their construction and performance, will be presented.