C_nH molecules are the simplest linear carbon chains in space. They are crucial for not only probes of young clouds but also benchmarks of calculations of chemical reaction network. However, their abundances occasionally show anomaly. For example, observed column densities of C₄H in various sources are one order of magnitude higher than theoretically estimated values. Herbst & Osamura suggested that these excesses of C₄H come from the theoretically determined dipole moment of C₄H.Herbst & Osamura, 2008, ApJ, 679, 1670. ^bWoon, 1995, Chem. Phys. Lett. 244, 45. ^cOyama et al., 2020, ApJ, 890, 39.he dipole moment in the electronic ground state of ²Σ⁺ was calculated to be 0.87 D by the RCCSD(T)/aug-cc-pVDZ level of ab initio theory.^b However, the mixing of wavefunctions between the ground state and the low-lying electronic excited state of ²Π having the large dipole moment of 4.4 D occurs, giving a higher dipole moment to the ground state. By using a higher dipole moment, a smaller column density is derived via observed line intensities. In the present study, we re-calculated the dipole moment of C₄H by quantum chemical calculations including the mixing.^c The calculations were carried out by the multi-reference configuration interaction level of ab initio theory using the cc-pVQZ basis set. The new dipole moment was derived to be 2.10 D, which is about 2.4 times larger than the value of 0.87 D used so far. Reported lines of C₄H were analyzed to revise column densities by using the new dipole moment. Revised values are about a factor of 6 smaller than those in the previous works. Using the revised column density of C₄H, abundances of the C_2nH (n = 1–4) series show exponential smooth decreases with carbon-chain length in various sources.

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Footnotes:

Herbst & Osamura, 2008, ApJ, 679, 1670. ^bWoon, 1995, Chem. Phys. Lett. 244, 45. ^cOyama et al., 2020, ApJ, 890, 39.T

Large difference of chemical compositions between molecular clouds and comets is a big question for astrochemistry. The case of a pre-biotic molecule CH₃NCO is one of them. The abundance ratio of [CH₃NCO]/[HNCO] is high in the comet 67P ( > 4, [1]), although it is low (0.02 − 0.3, e.g., [2]) in molecular clouds. An abundance of CH₃NCO is expected to be held and/or increased during evolutionary process of a cloud. A pair of an old core and a young core having the similar chemical compositions needs to be investigated for this evolutionary process. In this work, we aimed to detect CH₃NCO in the middle (M) core, which is relatively older than the north (N) core, in the Galactic Center star-forming region Sagittarius B2 with the 45 m telescope of Nobeyama Radio Observatory. The rotational transitions of J = 10 → 9 to 13 → 12 for CH₃NCO were detected in the 85 − 114 GHz region. The column density and the rotational temperature are derived to be N = (4.3 ± 2.1) × 10¹³ cm⁻² and T_rot = (32 ± 9) K, respectively, assuming local thermal equilibrium. Similarly, an abundance of HNCO is estimated to be N = (1.3 ± 0.5) × 10¹⁵ cm⁻² (T_rot = 21 ± 2 K), giving the ratio of [CH₃NCO]/[HNCO] = 0.032. Thus, as a simplest model, it is suggested that an abundance of CH₃NCO is held during evolutionary process of the Sagittarius B2 region.
[1] Goesmann et al., Science, 349, 689 (2015). [2] Halfen et al., ApJ, 812, L5 (2015).

Herein we present a laboratory rotational study of glycolamide (OHCH₂CONH₂) and an astronomical search for this molecule, a glycine isomer, and also one of the simplest peptide molecules that could reasonably be observed in the interstellar medium (ISM). Using a battery of state of the art rotational spectroscopic techniques in the frequency and time domain, L. Kolesniková, E. R. Alonso, S. Mata, and J. L. Alonso, APJS, 229 (2017), 26-34 and references therein.round 1500 transitions have been newly assigned. Based on the reliable frequency predictions, we report an accompanying radioastronomical search for glycolamide in the well known high-mass star forming region Sgr B2(N) using the ALMA imaging spectral line survey ReMoCA. A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, I. Medvedev, J. Thomas, Z. Kisiel, A&A, 628 (2019), A10.lycolamide was not detected in this source, and we report corresponding upper limits to the column density, showing that glycolamide is at least around 6 times less abundant than acetamide.M. Sanz-Novo acknowledges funding from a predoctoral FPU Grant (FPU17/02987).html:<hr /><h3>Footnotes: L. Kolesniková, E. R. Alonso, S. Mata, and J. L. Alonso, APJS, 229 (2017), 26-34 and references therein.a A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, I. Medvedev, J. Thomas, Z. Kisiel, A&A, 628 (2019), A10.G M. Sanz-Novo acknowledges funding from a predoctoral FPU Grant (FPU17/02987).

The project of Lille Spectroscopic Database 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, different codes were used: BELGIHougen, J. T. et al, 1994, J. Mol. Spec. 163, 559 RAM36Ilyushin, V.V. et al, 2010, J. Mol. Spec. 259, 26. ERHAMP. Groner, P. J. Chem. Phys. 107, 4483.r XIAMH.Hartwig H. et al, 1996, Z. Naturforsch 51a, 923.n the case of molecules with the internal rotation of a C_3v top, N. Ohashi code for the torsion-inversion problem of methylamineOhashi, N., et al. 1987, J. Mol. Spec., 126, 443 ASFIT/ASROTKisiel, Z. et al, 2019, J. Mol. Spec. 359, 16.rograms for simple asymmetric tops, and SPFIT/SPCATPickett H. M., 1991, J. Mol. Spec. 148, 371.rogram suite for the treatments of other tunneling motions. While the latter is the main fitting/predicting tool for widely known CDMS and JPL databasesMüller, H. S. P., et al., 2005, J. Mol. Spec. 327, 95; Pickett, H. M., et al., 1998, JQSRT 60, 883 spectral predictions obtained with other codes are somehow scattered in the supplementary data of publications and are eventually available in the another well known Splataloguehttps://splatalogue.onlineatabase. For this reason, we decided to develop and maintain the Lille Spectroscopic Database which will contain the spectral predictions of the molecules studied 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 also plan to make publicly available the rotational spectra recorded in Lille, and a tool (software) for their analysis. Hougen, J. T. et al, 1994, J. Mol. Spec. 163, 559, Ilyushin, V.V. et al, 2010, J. Mol. Spec. 259, 26., P. Groner, P. J. Chem. Phys. 107, 4483.o H.Hartwig H. et al, 1996, Z. Naturforsch 51a, 923.i Ohashi, N., et al. 1987, J. Mol. Spec., 126, 443, Kisiel, Z. et al, 2019, J. Mol. Spec. 359, 16.p Pickett H. M., 1991, J. Mol. Spec. 148, 371.p Müller, H. S. P., et al., 2005, J. Mol. Spec. 327, 95; Pickett, H. M., et al., 1998, JQSRT 60, 883, https://splatalogue.onlined

Applying various action spectroscopic techniques in a 4 K cryogenic ion trap instrument, protonated methanimine, CH₂NH₂⁺, has been investigated by high-resolution rovibrational and pure rotational spectroscopy for the first time. In total, 39 rovibrational transitions within the fundamental band of the ν₂ symmetric C-H stretch were measured around 3026 cm⁻¹, which were used to predict pure rotational transition frequencies of CH₂NH₂⁺ in the ground vibrational state. Based on these predictions, nine rotational transitions were observed between 109 and 283 GHz using a novel double resonance method. This method consists of rotational excitation followed by vibrational excitation, which is finally detected as a dip in the number of CH₂NH₂⁺-He complexes formed in the 4 K He bath of the trap.

Radical chemistry is thought to play a role in the formation of complex molecules in space, including nitrogen heterocycles and prebiotic species. Radical derivatives of pyridine, one of the simplest nitrogen heterocycles, have been suggested as key intermediates in barrierless pathways to the formation of nitrogen-containing polycyclic molecules. We have calculated the equilibrium geometries of the ortho-, meta-, and para-pyridyl radicals at the CCSD(T)/cc-pwCVTZ level of theory, along with nitrogen quadrupole and hyperfine interaction terms. Spin-rotation terms were calculated at CCSD(T)/cc-pwCVDZ. Vibrational corrections to the rotational constants have also been evaluated at the CCSD(T)/cc-pwCVDZ level using second-order vibrational perturbation theory. We will discuss the results of these calculations as well as efforts to obtain the rotational spectra of these radicals using Fourier transform microwave spectroscopy.

Oxiranecarbonitrile (cyano-oxirane, c-C₂H₃OCN) is of interest as a possible chiral precursor molecule of evolutionM. Bolli, R. Micura, A. Eschenmoser, Chem. Biol., 1997, 4, 309 (and refs. cited therein).. We have calculated parity violation in this moleculeR. Berger, M. Quack, G. Tschumper, Helv. Chim. Acta., 2000, 83, 1919. in view of possible experiments and biomolecular homochiralityM. Quack, Chem. Phys. Lett. 1986, 132, 147; M. Quack, Angew. Chem. Intl. Ed., 2002, 41, 4618.. The spectrum of the molecule has been investigated in the millimeter, submillimeterM. Behnke, I. Medvedev, M. Winnewisser, F. C. De Lucia, and E. Herbst, ApJ. Supplement Series, 2004, 152, 97. and terahertzS. Albert, Ph. Lerch, K. Keppler and M. Quack, Proceedings of the XX. Symposium on Atomic, Cluster and Surface Physics 2016, (SASP 2016), Innsbruck University Press (2016), pp. 165−168 (and refs. cited therein). regions. Here we report high resolution (0.0011 cm⁻¹) measurements of the infrared spectrum of this molecule at room temperature using the Zurich Prototype ZP 2001 FTIR Spectrometer, and a rovibrational analysis of about two thousand transitions associated with the ν₁₂ (915.3 cm⁻¹) and ν₁₃ (848.2 cm⁻¹) fundamentals using a Watson Hamiltonian and the WANG programD. Luckhaus and M. Quack, Mol. Phys., 1989, 68, 745; S. Albert, K. Keppler Albert, H. Hollenstein, C. Manca Tanner, M. Quack in "Handbook of High Resolution Spectroscopy," M. Quack and F. Merkt, Eds., 2011, Vol. 1, Chapter 3, pp. 117-173, Wiley, Chichester., including also molecular parameters and ground state energies from our work in the THz region^e. Accurate spectroscopic parameters were obtained. The results are discussed in relation to astrophysical spectroscopic searches and the evolution of biomolecular homochirality R. Berger, M. Quack, G. Tschumper, Helv. Chim. Acta., 2000, 83, 1919.M. Behnke, I. Medvedev, M. Winnewisser, F. C. De Lucia, and E. Herbst, ApJ. Supplement Series, 2004, 152, 97.D. Luckhaus and M. Quack, Mol. Phys., 1989, 68, 745; S. Albert, K. Keppler Albert, H. Hollenstein, C. Manca Tanner, M. Quack in "Handbook of High Resolution Spectroscopy," M. Quack and F. Merkt, Eds., 2011, Vol. 1, Chapter 3, pp. 117-173, Wiley, Chichester.

A wide variety of nitrogen-containing heterocycles have been detected on meteorites with non-terrestrial isotopic abundances, indicative of an interstellar origin. However, no N-heterocycles have been detected in space and their formation pathways are unclear. Experimental work has shown that N-heterocycles can likely form through barrierless radical-neutral gas-phase reactions, which are feasible in the low temperature environments of cold molecular clouds and the outer regions of protoplanetary disks. Astronomical searches for potential precursors and depletion products are critical to determining if such mechanisms play a role in N-heterocycle formation. Here, calculated CCSD(T)/pwCVTZ equilibrium geometries and progress towards measuring and assigning the 5 - 40 GHz rotational spectra of three pyrrolyl isomers () will be discussed. Pyrrolyl is both a photodissociation product of the N-heterocycle pyrrole () and a potential precursor to larger N-heterocycles. This work will enable astronomical searches, spectroscopy in higher frequency bands, and kinetics and dynamics studies.

Nitrogen-containing heterocycles pose an intriguing astrochemical mystery. 45 different varieties have been detected on meteorites with non-terrestrial isotopic abundances, but none have been detected in space despite numerous search attempts. It is unclear if these species are most likely to form through low-temperature gas-phase chemistry, photoprocessing of icy grains, aqueous chemistry in a meteorite parent body, or a combination of processes. Reactions involving radicals have recently shown promise as N-heterocycle formation mechanisms, particularly in low temperature gas-phase chemistry. We have used an ab initio molecular dynamics "nanoreactor" simulation developed for chemical reaction discovery to reveal multiple novel gas-phase N-heterocycle formation pathways from nonintuitive molecular precursors. Many reactants identified in the simulations are similar to known interstellar molecules but have not specifically been studied with rotational spectroscopy, precluding astronomical searches and warranting further experimental and theoretical study. These simulations also reinforce previous experimental and theoretical studies which have shown that smaller N-heterocycles may serve as precursors to larger ones. This type of computational investigation may be a useful tool for furthering our understanding of chemistry in the interstellar medium.

Searches have been conducted for the J=2-1 transitions of methanol at 3mm in a sample of molecular clouds located 13-23.5 kpc from the Galactic Center, using the ARO 12m telescope. The sources are in the Cygnus arms, and typically are cold with T_K approximately 20 K. Multiple transitions of this organic molecule were detected in 19 clouds, including ones at distances of approximately 23.5 kpc. Typical abundances found for methanol are 1x10⁹. The results suggest that the Galactic Habitable Zone (GHZ) may exist much further from the Galactic Center than previously thought.

The millimeter-wave spectrum of the SiP radical in its X²Π_i ground electronic state has been recorded using direct absorption spectroscopy in the frequency range 151 – 532 GHz. The species was synthesized in an AC discharge by the reaction of SiH₄ and red phosphorous, in argon carrier gas. Both lambda-doubling and hyperfine splittings, from the phosphorus nuclear spin (I = 1/2), were observed in both spin-orbit ladders, Ω = 3/2 and 1/2. The Ω =1/2 ladder appears to be perturbed, presumably by the nearby A²Σ state, as suggested by previous optical data. The data were analyzed with a Hund’s case (a) Hamiltonian, establishing global spectroscopic constants. A deperturbation analysis was also conducted, further refining the Π-Σ interaction.