Cyclopropanone is a fundamental, strained organic compound as the smallest cyclic ketone. It is also a potential astrochemical molecule that has been reported by Abplanalp et al. in 2015 to form on ices consisting of carbon monoxide and ethylene when bombarded by high-energy electrons.¹ Despite this, searches for cyclopropanone in the interstellar medium has been hampered by a lack of available rotational data beyond 40 GHz. Its microwave spectrum has been studied previously by Flygare and coworkers in 1969, who reported 15 transitions and determined its rotational constants.² Its rotational spectrum has not been reinvestigated, presumably due to the difficulty of obtaining a pure sample. Recently, we have been able to produce cyclopropanone from ketene and diazomethane in diethyl ether. Herin, we report, the rotational spectra of cyclopropanone from 85-750 GHz and a least-squares fit of its ground state using A- and S-reduction, sextic, centrifugally distorted Hamiltonians. Likewise, we have measured, assigned and least-squares fit transitions for the four lowest energy vibrationally excited states. The two lowest energy fundamentals (ν₁₈, ν₁₄) have been adequately fit to single-state Hamiltonians. The next fundamental (ν₉) and first overtone presented in this work (2ν₁₈) exhibit perturbed frequencies due to Coriolis and anharmonic coupling. The current progress towards satisfactory treatments of these interactions will be presented. [1]M. K. Abplanalp, A. Borsuk, B. M. Jones, R. I. Kaiser, Apj. 2015, 814, 45. [2]J. M. Pochan, J. E. Baldwin, W. H. Flygare, J. Am. Chem. Soc. 1969, 91, 8, 1896-1898

Acetaldoxime (acetaldehyde oxime, , ) is a small molecule potentially relevant to prebiotic chemistry in the ISM. The rotational spectra of its two conformers and multiple isotopologues have been previously reported in the region 8-40 GHz by Rogowski and SchwendemanRogowski, R. S.; Schwendeman, R. H. J. Chem. Phys. 1969, 50, 397–403nd Hosoi et al.Hosoi, K.; et al. J. Mol. Struct. 2005, 735-736, 325–334ith the goal of enabling broader astronomical searches, we have extended the rotational spectrum of acetaldoxime over the region 70-700 GHz using a 2 m direct absorption flow cell at room temperature. Here we present the spectrum of acetaldoxime and the results of the ongoing analysis.

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Rogowski, R. S.; Schwendeman, R. H. J. Chem. Phys. 1969, 50, 397–403a Hosoi, K.; et al. J. Mol. Struct. 2005, 735-736, 325–334W

Deuterium fractionation is an important tool for tracing the chemical history and inheritance of molecules throughout star and planet formation. While there has been an increased focus on the detection of deuterated oxygen-containing complex organic molecules (COMs), the community is yet to identify a deuterated isotopologue of a sulphur-based COM. This leaves many questions related to the formation and evolution of sulphur COMs and their relation to oxygen chemistry unanswered. The simplest sulphur-containing COM is methyl mercaptan, CH₃SH, that has been detected in both low- and high-mass star forming regions with abundances that make the detection of its deuterated isotopologues, plausibleDrozdovskaya, M. N., et al. MNRAS 476.4 (2018): 4949-4964. We have collected the millimetre spectrum of CH₂DSH and CHD₂SH from 80 to 500 GHz, which will provide the necessary spectral information for their detection in the interstellar medium (ISM). The spectra, however, are complicated by the hindered torsional rotation of the CH₂D/CHD₂ group. The Hamiltonian needed to account for this unsymmetrical methyl rotor requires an accurate potential which is extracted from far infrared torsional subbands recorded using the high-resolution facilities at the Canadian Light Source and SOLEIL. We have assigned more than 2000 millimetre transitions for the singly deuterated isotopologue including a-type R-branch, b-type Q-branch, and inter-state transitions for all three substates. Additionally, we have identified and begun fitting the doubly deuterated isoptologue. We will present an update on the spectral analysis of these complex spectra, along with our attempts to identify them towards the protostellar region IRAS16293.

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Drozdovskaya, M. N., et al. MNRAS 476.4 (2018): 4949-4964..

Chlorinated species have been detected in various extraterrestrial environments, such as the interstellar medium (ISM), Mars, and carbonaceous chondrites. In the ISM, more than 90% of known chlorine is found in HCl, which is predicted to react with other known ISM constituents, ethylene oxide (c-CH₂CH₂O) and 1,2-ethanediol (HOCH₂CH₂OH), to form the simplest stable organic chlorohydrin, 2-chloroethanol (ClCH₂CH₂OH).¹ The detection of 2-chloroethanol is therefore critical for modeling chlorine chemistry in the ISM and guiding future astronomical observations. To assist the detection of 2-chloroethanol in the ISM, the rotational spectrum of 2-chloroethanol was measured from 140 to 700 GHz, coinciding with the frequency ranges for radio telescopes like ALMA and NOEMA. Additional microwave spectra from 8 to 26 GHz were collected to provide new measurements of rotational transitions with resolved quadrupole coupling. Both chlorine isotopologues (³⁵Cl and ³⁷Cl) were observed for the lowest-energy gauche-gauche conformer, providing an improved set of rotational and centrifugal distortion constants up to the octic level, for the ground and several vibrationally excited states less than 500 cm⁻¹. Recent analysis of the ³⁷Cl isotopologue has resolved and refined the nuclear quadrupole coupling constants. Here, we will present an update of our spectral analysis for this potentially important interstellar species.
¹ Soliday, R. M.; Bunn, H.; Sumner, I.; Raston, P. L. Far-Infrared Synchrotron Spectroscopy and Quantum Chemical Calculations of the Potentially Important Interstellar Molecule, 2-Chloroethanol. JPCA 2019, 123 (6), 1208–1216. https://doi.org/10.1021/acs.jpca.8b11333.

Methoxy-substituted heterocycles exhibit strong conformational preferences dependent on heteroatom identity, reflecting a subtle balance of intramolecular interactions. In this study, we investigated the conformational landscapes of 2-methoxyfuran and 2-methoxythiophene by chirped-pulse Fourier transform microwave spectroscopy and quantum chemistry. We confirm that the anti-coplanar geometry of the methoxy group represents the lowest energy confirmation for both species. However, our computational results find significant differences between their second lowest energy conformations and that the barrier to methyl internal rotation is strongly modified by the orientation of the methoxy group.

Optically centrifuged carbon dioxide molecules are investigated using high resolution transient IR absorption spectroscopy. A tunable optical centrifuged is used prepare an ensemble of molecules in rotational states up to J=280. New (0001)-(0000) IR transition frequencies are measured for R-branch transitions of J=186-282 and compared with effective Hamiltonian calculations. Evidence for two spectral perturbations are observed above J=241 in the (0001) vibrational state coming from interactions with the (0330) and (1001) states. Polarization-sensitive transient IR probing is used to measure J-dependent populations, polarization anisotropy, and collisional relaxation rates. Doppler-broadened transient line profiles show that the centrifuged molecules are prepared with low translational energies and that collisions of high-J molecules with thermal bath molecules lead to large translational energies in the collision products. Polarization analysis gives information about the alignment of molecules in the optical centrifuge field and yields initial mJ values.

We re-investigate the ν₃-ν₆ Coriolis interaction in CF₃I as part of the testing and evaluation of a newly constructed chirped-pulse Fourier-transform microwave (CP-FTMW) spectrometer in the 2-8 GHZ region. We observe vibrational satellites and ¹³C peaks in natural abundance. We report low-J vibrational satellites for the ν₆ level for the first time. The observed frequencies deviate significantly from the prediction of of the fit model reported by Walters and Whiffen Walters, S.W. and D.H. Whiffen, Rotational spectrum of trifluoroidomethane. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 1983. 79(6): p. 941-949.nd more recently by Willeart et al.,Willaert, F., et al., High resolution investigation of the v3 band of trifluoromethyliodide (CF3I). Journal of Molecular Spectroscopy, 2015. 315: p. 16-23.hich motivates us to re-evaluate the fit model using the combined dataset of microwave and millimeter-wave transition frequencies. The results of our fit to the combined dataset will be presented. The analysis allows us to make an improved determination of ν₆ frequency, which has never been observed directly by IR spectroscopy.

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Walters, S.W. and D.H. Whiffen, Rotational spectrum of trifluoroidomethane. Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics, 1983. 79(6): p. 941-949.a Willaert, F., et al., High resolution investigation of the v3 band of trifluoromethyliodide (CF3I). Journal of Molecular Spectroscopy, 2015. 315: p. 16-23.w

Prior work in our laboratory has characterized the reaction between SO₃ and carboxylic acids to form carboxylic sulfuric anhydrides. In this study, this chemistry is shown to extend to thiocarboxylic acids. Thiobenzoic acid, C₆H₅COSH, was combined with sulfur trioxide in a supersonic jet using an on-the-fly mixing nozzle in which C₆H₅COSH vapor was introduced through a hypodermic needle into an Ar/SO₃ expansion. The product species, C₆H₅C(=S)OSO₂OH, was observed by Fourier transform microwave spectroscopy and its identity was confirmed by isotopic substitution as well as agreement with M06-2X/6-311++G(d,p) calculations. The calculations further indicate that the reaction is energetically favorable: the SO₃·C₆H₅COSH complex is 15.2 kcal/mol lower in energy than C₆H₅COSH + SO₃ at infinite separation, and the anhydride product is 3.6 kcal/mol below that. The barrier to anhydride formation, starting with the complex, is 4.5 kcal/mol. Clearly, the anhydride forms rapidly in the jet, as the collisional phase of the expansion only lasts for several tens of microseconds.

Since its development nearly 20 years ago, chirped-pulse Fourier transform microwave spectroscopy has dramatically changed the landscape of rotational spectroscopy. Its large bandwidth compared with cavity Fourier transform and frequency-modulation instruments affords a massive reduction in the time required to acquire spectra over a wide frequency range. Chirped-pulse instruments have been developed from the microwave through the millimeter wave spectral regions, and each instrument typically involves a unique combination of hardware (oscilloscopes, high-speed digitizers, waveform generators, etc), yet software for integrating these components into a common workflow has not been readily available. In this talk, I will introduce BlackchirpBlackchirp and its documentation are available at https://github.com/kncrabtree/blackchirp an open-source, cross-platform (Windows, Mac, Linux) program designed to facilitate the acquisition of chirped-pulse data and which is currently used to control instruments at UC Davis, Harvey Mudd College, MIT, and the Harvard-Smithsonian Center for Astrophysics. Blackchirp has a modular architecture which supports many possible combinations of hardware, and new devices can be incorporated into the program with a small amount of C++ knowledge. It supports the traditional wideband acquisition mode as well as segmented LO-scanning acquisitions, and the collected data are displayed in an interactive format in real time during the acquisition. A Python package is available for reading in FID data collected by the program and for performing common processing tasks. This talk will provide an overview of Blackchirp's functionality and how to adapt the program to new hardware devices.

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Blackchirp and its documentation are available at https://github.com/kncrabtree/blackchirp,

Microwave-microwave double resonance (MMDR) spectroscopy is a type of two-dimensional spectroscopy that identifies pairs of rotational transition frequencies that share a quantum state. MMDR spectra are an effective tool for identifying transition ladders in a rotational spectrum, and, qualitatively, they can provide insight into molecular asymmetry and the strength of cartesian dipole componentsMartin-Drumel et al. 2016 JCP 144, 124202 In this work, a set of convolutional neural network (CNN) classification and regression models are trained to predict non-zero dipole components and ratios of principal rotational constants from MMDR spectra. Like many deep learning methods, training CNN models requires a large set of labeled training data which precludes their usefulness in many spectroscopy applications. Here, the CNNs are trained on datasets of simulated rigid rotor MMDR spectra created with Pickett’s SPCAT and randomly generated sets of the principal rotational constants: A, B, and C. Preliminary results show that, with a sufficiently dense MMDR spectrum, the models frequently predict the correct non-zero dipole components and can determine the C/B and C/A ratios with RMSEs of 0.1 and 0.05.

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Martin-Drumel et al. 2016 JCP 144, 124202.