Recently, cyclic molecules such as benzonitrile B.A. McGuire, A.M. Burkhardt, S. Kalenskii, C.N. Shingledecker, A.J. Remijan, E. Herbst, M.C. McCarthy, Science 359, 202 (2018).nd 2-cyanocyclopentadiene M.C. McCarthy, K.L.K. Lee, R.A. Loomis, A.M. Burkhardt, C.N. Shingledecker, S.B. Charnley, M.A. Cordiner, E. Herbst, S. Kalenskii, E.R. Willis, C. Xue, A.J. Remijan, B.A. McGuire, Nat. Astron. 5, 176 (2021).ave been discovered in the interstellar medium. Cyclic molecules with large dipole moments are considered good candidates for future search. Isothiazole (C₃H₃NS) is a five-membered ring molecule with two adjacent hetero atoms, nitrogen and sulfur. Previous studies of millimeter-wave spectroscopy have been conducted below 35 GHz J.H. Griffiths, A. Wardley, V.E. Williams, N.L. Owen, and J. Sheridan, Nature 216, 1301 (1967).^,J. Wiese, D.H. Sutter,Z. Naturforsch. A 35, 712 (1980).^, . Gripp, U. Kretschmer, H. Dreizler Z. Naturforsch. A 49, 1059 (1994). and data at higher frequencies are desired. Therefore, we performed a new measurement in the region of 40-360 GHz at room temperature. The ground state, and the vibrational excited states (ν₁₈=1, ν₁₇=1, ν₁₃=1, ν₁₆=1, ν₁₂=1, ν₁₁=1, ν₁₅=1, ν₁₀=1, and ν₁₄=1) were analyzed by using AABS Z. Kisiel, L. Pszczókowski, I. R. Medvedev, M. Winnewisser, F. C. De Lucia, E. Herbst, J.Mol.Spectrosc. 233, 231 (2005). and SPFIT/SPCAT H. M. Pickett, J.Mol.Spectrosc. 148, 371 (1991).ackages. More than 10000 lines were assigned and analyzed using Watson’s A-reduced Hamiltonian.

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Footnotes:

B.A. McGuire, A.M. Burkhardt, S. Kalenskii, C.N. Shingledecker, A.J. Remijan, E. Herbst, M.C. McCarthy, Science 359, 202 (2018).a M.C. McCarthy, K.L.K. Lee, R.A. Loomis, A.M. Burkhardt, C.N. Shingledecker, S.B. Charnley, M.A. Cordiner, E. Herbst, S. Kalenskii, E.R. Willis, C. Xue, A.J. Remijan, B.A. McGuire, Nat. Astron. 5, 176 (2021).h J.H. Griffiths, A. Wardley, V.E. Williams, N.L. Owen, and J. Sheridan, Nature 216, 1301 (1967).\end J. Wiese, D.H. Sutter,Z. Naturforsch. A 35, 712 (1980). . Gripp, U. Kretschmer, H. Dreizler Z. Naturforsch. A 49, 1059 (1994)., Z. Kisiel, L. Pszczó kowski, I. R. Medvedev, M. Winnewisser, F. C. De Lucia, E. Herbst, J.Mol.Spectrosc. 233, 231 (2005)., H. M. Pickett, J.Mol.Spectrosc. 148, 371 (1991).p

The cyanomethyl radical, CH₂CN, is considered a key reactive intermediate in the interstellar medium (ISM) since its first detection [1]. To date, the radical has been detected in several environments of the ISM using pure rotational data available in the literature, limited to frequencies below 280 GHz [2,3]. The radical is also postulated to participate to the formation of complex organic molecules, such as cyanoacetaldehyde [4]. To enable the detection of the CH₂CN radical in current high frequency astronomical surveys, laboratory re-investigation of its spectrum at submillimeter wavelengths appears essential. We have investigated the pure rotational spectrum of CH₂CN at room temperature in the 75-900 GHz domain. The radical was produced using a H-abstraction method from CH₃CN using F atoms. To record pure rotational transitions, we used two spectrometers: a commercial broadband chirped-pulse (CP) spectrometer covering the 75-110 GHz spectral region and a tunable single-frequency absorption spectrometer exploiting a frequency multiplication chain with a large spectral coverage (here, 140-900 GHz). A combined fit of the literature data and our newly measured transitions (involving N’’ and K_a’’ up to 42 and 8, respectively) yields to an improvement of the rotational parameters; in particular the A rotational constant and K-dependent parameters. This work allows for confident searches of the radical in cold to warm environments of the ISM, over a wide frequency range. In addition, the broadband capacities of the CP spectrometer has also revealed very efficient in the study of discharge products (synthesized by the reaction between CH₃CN and F atoms in this work). I will present both aspects of this work: the improvement of the spectroscopy of CH₂CN and the analysis of the chemical composition of the discharge by CP spectroscopy. [1] W. M. Irvine et al., The Astrophysical Journal Letters (1988) 334, L107 [2] S. Saito et al., The Journal of Chemical Physics (1997) 107, 1732 [3] H. Ozeki et al., American Astronomical Society (2004) 617, 680 [4] B. Ballotta et al., ACS Earth and Space Chemistry (2021) 5, 1071

Five- and six-membered aromatic rings have received significant attention in the exploration of interstellar space. Not only have recent detections expanded our understanding of interstellar chemistry but also highlight the timeliness and importance of investigation of the laboratory rotational spectra of such molecules. Following the detections of cyclopentadiene¹ and benzene² via rotational and infrared spectroscopies, respectively, their respective nitrogen containing analogues, pyrrole (C₄H₅N) and pyridine (C₅H₅N), call for extensive investigation of their rotational spectra as well as their chemistry under harsh energetic conditions. Here, we present a detailed study of the products of pyrrole (C₄H₅N) and pyridine (C₅H₅N) generated through electrical discharge of the precursors and supersonic expansion. The spectra of the resulting species are simultaneously recorded with a Chirped Pulse Fourier Transform Microwave (CP-FTMW) Spectrometer operating in the 18-26 GHz frequency region.³ The observed species, varying from cyclopropene to linear cyanopolyynes, contain both fewer and more, or the same number of carbons as their respective precursors suggesting that both fragmentation and recombination processes take place during electrical discharge. Our results support the detection of related molecules in the interstellar medium which may also provide an insight into potential pathways around their formation. ¹ Cernicharo, J., Agúndez, M., Cabezas, C., Tercero, B., Marcelino, N., Pardo, J. R. & de Vicente P. A&A. 649, L15 (2021) ² Cernicharo, J., Heras, A. M., Tielens, A. G. G. M., Padro, J. R., Herpin, F., Guelin, M. & Waters, L. B. M. Astrophys. J. 546, L123 (2001) ³ Fatima, M., Perez, C., Arenas, B. E., Schnell, M. & Steber, A. Phys. Chem. Chem. Phys. 22, 17042-17051 (2020)

The molecular universe of Astrochemistry is expanding at a surprisingly rapid pace. However, to univocally identify the transitions of the studied molecule within an astronomcial survey -which are, typically, densely packed with lines- an extremely accurate knowledge of the rotational frequencies is required. Therefore, an accurate spectroscopic characterization of E- and Z-cyanovinylacetylene (CVA), allenylacetylene (AA) and propadienone (PD) has been carried out to guide their detection in the interstellar medium. An eventual first detection, as it would be for PD and Z-CVA, as well as new findings (on E-CVA and AA, which have been recently identified in TMC-1) in different astronomical regions, can be of great help in the refining of the models of the interstellar objects. Indeed, PD is the only isomer of the [H₂C₃O] family which has not been observed in the ISM, while unsaturated carbon chains like CVA and AA can play important roles in reactivity, e.g., the pathways leading to the formation of aromatic molecules. In this work, we relied on a solid computational study to complete the experimental data available in literature. The accurate equilibrium geometries of the four species have been determined, exploiting composite schemes rooted in the coupled-cluster theory. Harmonic and anharmonic force field calculations gave access to the set of centrifugal distortion parameters; the importance of an accurate estimate of the sextic ones is presented. Exploiting a pyrolysis system to generate the four species in the gas-phase and using a frequency-modulation spectrometer working in the millimeter/sub-millimeter wave range, we were able to record and analyze the rotational spectrum up to 400 GHz, providing accurate rotational frequencies and a thorough characterization of the spectroscopic parameters.

l0pt Figure Being N-substituted unsaturated species, azabutadienes are molecules of potential relevance in astrochemistry, ranging from the interstellar medium to Titan's atmosphere. 2-azabutadiene and butadiene share a similar conjugated π system, thus allowing the investigation of the effects of heteroatom substitution. More interestingly, 2-azabutadiene can be used to proxy the abundance of interstellar butadiene. To enable future astronomical searches, the rotational spectrum of 2-azabutadiene has been investigated up to 330 GHz. Experiment has been supported and guided by an accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the two possible forms, trans and gauche. The trans species, more stable by about 7 kJ/mol than gauche-2-azabutadiene, has been experimentally observed and its rotational and centrifugal distortion constants obtained with remarkable accuracy, while theoretical estimates of the spectroscopic parameters are reported for gauche-2-azabutadiene.

3-hydroxypropanamide (HOCH₂CH₂CONH₂), has primarily been used in drug synthesis and is an isomer of the amino acid β-alanine. Due to its structural similarity to β-alanine, it is a key target for tracing the formation of important biomolecules in astrochemistry. 3-hydroxypropanamide has a low vapor pressure and readily decomposes when heated to temperatures above  ∼ 80^°C. Therefore, no rotational spectroscopic investigation has yet been conducted. We report the rotational spectrum of 3-hydroxypropanamide collected from 140-460 GHz using a long-pathlength direct absorption millimeter/submillimeter spectrometer. To aid in its characterization, the gas sample was held at a static pressure of  ∼  40 mTorr at 70 ^°C; these conditions could be held for several hours so that broadband spectra could be acquired. We will report in this talk on the 3-hydroxypropanamide spectra obtained and the progress of spectral analysis.

2-Chloroethanol (HOCH₂CH₂Cl) is the smallest terrestrially stable chlorohydrin and is predicted to exist in the interstellar medium, forming from HCl with either oxirane or ethylene glycol, each of which are known interstellar constituents. RotationalAzrak, R. G.; Wilson, E. B. The Journal of Chemical Physics, 1970 52 (10), 5299–5316nd ro-vibrational Soliday, R. M.; Bunn, H.; Sumner, I.; Raston, P. L. The Journal of Physical Chemistry A, 2019 123 (6), 1208–1216^, Hull, K.; Soliday, R. M.; Raston, P. L. Journal of Molecular Structure, 2020, 1217:128369pectra of 2−chloroethanol have been previously reported from 9−40 GHz and 100−500 cm^-1, respectively. However, attempts at the detection of 2−chloroethanol towards Sgr B2(N) have been unsuccessful. It is uncertain if the lack of detection arises from its lack of presence in this sightline, or whether the extrapolated spectral information for 2−cholorethanol is not of sufficient accuracy to guide astronomical searches. Therefore, we have measured the spectrum of 2−chloroethanol from 140 to 700 GHz to further improve the molecular constants and provide spectral frequencies directly comparable to radio telescope data. Analysis of this spectrum has resulted in the determination of refined rotational constants and centrifugal distortion constants up to the octic level for both naturally occurring Cl isotolopologues. Partially resolved nuclear quadrupole coupling arising from the presence of the chlorine atom is observed throughout the spectral range. New spectra from 8 to 26 GHz have been obtained to refine the quadrupole coupling constants with well resolved microwave transitions. We also have tentative least−squares fits of transitions for all vibrationally excited states below 500 cm^-1 Hull, K.; Soliday, R. M.; Raston, P. L. Journal of Molecular Structure, 2020, 1217:128369s

cis-3-Hexenal (c3-HA; O=CH-CH₂-CH=CH-CH₂-CH₃) is known as an odor molecule of grass and the c3-HA easily isomerizes to trans-2-hexenal (t2-HA). Rotational spectra of the c3-HA and its structural isomers were observed by Fourier transform microwave (FTMW) spectroscopy in the frequency region 4.8-23 GHz. We reported that two conformers of the c3-HA, SG’cS and CScS, were assignedS. Yoshizawa, N. Kuze and Y. Kawashima, ISMS2019, P3866 (2019). in SG’cS, S, G’, c, and S in order denote the skew, gauche’, cis and skew around the dihedral angles OC(1)C(2)C(3), C(1)C(2)C(3)=C(4), C(2)C(3)=C(4)C(5) and C(3)=C(4)C(5)C(6), respectively. We found other four conformers which were assigned to the SStS and S’S’tS conformers of trans-3-hexenal (t3-HA), and the TcSG’ and TcST conformers of cis-2-hexenal (c2-HA) by comparing from the results of ab initio calculation. We also observed the rotational spectra of the t2-HA which had been reported in 2015R. Yokoyama, Y. Kawashima, and E Hirota, 9th Annual Meeting on Molecular Science, Tokyo, 4P008 (2015). The spectra of the c3-HA and t3-HA were observed in room temperature. When the nozzle temperature increased, the maximum of spectral intensities of the c3-HA and t3-HA reach at around 350 K while the intensities of the t2-HA and c2-HA are stronger. This evidence shows that the c3-HA and t3-HA isomerized into the t2-HA and c2-HA.

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S. Yoshizawa, N. Kuze and Y. Kawashima, ISMS2019, P3866 (2019).: R. Yokoyama, Y. Kawashima, and E Hirota, 9th Annual Meeting on Molecular Science, Tokyo, 4P008 (2015)..

High level ab initio calculations at the CCSD(T)//MP2/6-311++ level were used to model the rotational constants and hyperfine constants of 2-iodoethanol. A potential energy surface scan was performed at the B3LYP/6-311G++ level of theory to obtain a better understanding of the conformational landscape and possible conformations. The B3LYP/6-311G++ level of theory was also used to calculate centrifugal distortion constants and zero-point vibrational corrections. We report for the first time the rotational spectroscopic observation on the gauche hydrogen bonding conformer of 2-iodoethanol using a molecular beam, cavity-based Fourier transform microwave spectrometer in the frequency range of 9.4-18.0 GHz. A semi-rigid rotor Hamiltonian perturbed by nuclear quadrupole hyperfine interactions was used to fit the spectrum. 20 rotational transitions split into 104 hyperfine components by the 5/2 nuclear spin of iodine have been measured. A least-squares fit of 3.9 kHz provided the fitted rotational constants which are A = 11369.8531(10), B = 1833.107(5), C = 1654.322 (5) MHz, and the nuclear quadrupole coupling constants which are χ_aa = -1476.693(9) MHz, χ_bb-χ_cc = -189.0537(2) MHz, χ_ab = -1180.354(12) MHz, χ_ac = 332.17(6) MHz, and χ_bc = 243.862(24) MHz. The spectrum of 2-iodoethanol is consistent with the theoretical model structure which predicts a 2.91Å intramolecular hydrogen bond.

The rotational spectra of several new silicon-bearing carbon chains were detected by means of Fourier-transform microwave spectroscopy in a supersonic jet source equipped with an electrical discharge. The newly detected species are HSiCCH, H₂C₃Si, and the SiC₅H radical. Precise rotational constants have been determined for all three, and as have fine and hyperfine constants for SiC₅H. Using samples enriched in carbon-13 and D, it has also been possible to detect several rare isotopic species and in turn derive an experimental structure for HSiCCH. Isotopic spectroscopy also provides clues as to the formation pathways that may be operative in our discharge. Finally, because these chains are both polar and closely related in structure and composition to other small Si-bearing chains and rings that have been detected in the circumstellar envelope of the evolved carbon star IRC+10216, they may be of astronomical interest.

The ongoing development of rotational spectroscopy through the growth of broadband capabilities and automated acquisition schemes regularly generates a wealth of data to be analyzed. However, assigning these data is often a bottleneck to obtaining useful chemical information. This is particularly true for unknown carriers for which no initial guess or constraint is available. Development of automated spectral analysis tools is therefore critical to fully utilize rotational spectroscopy data. We have previously reported the development of a high speed algorithm for the calculation of asymmetric rotor spectra. Previous versions of this software included basic search and assignment features that were capable of producing a list of probable matches that can be readily evaluated by hand. Since its original release, we have added several new features, including more advanced and automated searching, significant performance increases, multithreading support, and new calculation types. We will discuss the program, improvements, and implementation of its new features.