Urea has an important role in the nitrogen cycle of organisms and is produced at large scales industrially for food production among other uses. Its significance in the formation of complex prebiotic molecules has made it an appealing target for astronomers searching for precursors to life in space [1]. Some of the data presented here has enabled definitive detection of urea in the interstellar medium with modern submillimeter telescopes [2]. Assignment of the ground and eight lowest vibrational states of urea, (NH₂)₂CO, was performed over a spectral range between 210-500 GHz [3]. Intensities of the excited state lines were calibrated by means of a global fit of the ground state and excited state intensities to determine relative vibrational energies. The lowest of these states was found to be  61 cm⁻¹above the ground state which is consistent with previously determined values and could potentially aid in the determination of the temperature urea spectra. The next two lowest vibrational states we found to be significantly coupled and were treated with a Coriolis coupling model. Other higher vibrational states also demonstrated significant coupling. Combined, the vibrational symmetries along with the relative energies provide insight into the structure of urea vibrational energies. [1] A. J. Remijan et al., “OBSERVATIONAL RESULTS OF A MULTI-TELESCOPE CAMPAIGN IN SEARCH OF INTERSTELLAR UREA [(NH2)2CO],” Astrophys J, vol. 783, no. 2, p. 77, 2014, doi: 10.1088/0004-637X/783/2/77. [2] A. Belloche et al., “Re-exploring Molecular Complexity with ALMA (ReMoCA): interstellar detection of urea,” Astron & Astrophys, vol. 628, 2019, . Available: https://doi.org/10.1051/0004-6361/201935428 [3] D. J. Tyree, T. W. Chapman, I. R. Medvedev, and Z. Kisiel, “Rotational spectroscopy of urea up to 500 GHz: The ground and eight excited vibrational states,” J Mol Spectrosc, vol. 390, p. 111706, 2022, doi: https://doi.org/10.1016/j.jms.2022.111706.

The bands of LaO appear prominently in the spectra of cool S-type stars and can be used to determine La abundances. We have rotationally analyzed the LaO A²Π-X²Σ⁺ band system up to v=3 in the excited state using PGOPHER. The spectroscopic constants for the ground state were taken from our previous analysis of B²Σ⁺-X²Σ⁺ band system [1]. The band and equilibrium constants for the A²Π state were determined. RKR potentials were calculated and band strengths were obtained using LeRoy's LEVEL program with an ab initio transition dipole moment. This work also provides calculated radiative lifetimes for v=0 to v=3 of the A state. A line list for the LaO A²Π-X²Σ⁺ transition is provided which can be used to simulate LaO spectra in S-type stars.
1. P. F. Bernath, R. Dodangodage and J. Liévin, S-type stars: LaO line list for the B²Σ⁺ - X²Σ⁺ band system, Astrophys. J. 933, 99 (2022).

Ozone is a common retrieval target from a variety of remote sensing platforms owing to both its importance in tropospheric and stratospheric chemical processes and readily accessible observation grade absorption/emission bands in the THz, infrared, visible, and ultraviolet. Refinement of the ν₃ band line intensities in the 10 micron region has been the target of many spectroscopic studies in the past decades with uncertainty claims now approaching the 1% level. These studies typically constrain experimental ozone number density using UV cross section measurements while simultaneously performing Fourier transform or laser-based measurements in the infrared. This talk will summarize ongoing efforts to perform dual band measurements using a mode-hop-free quantum cascade laser in the infrared that instead derives ozone partial pressures from simultaneously collected direct absorption spectra in the sub-millimeter (500-600 GHz) region. This alternative approach, which serves as the first sub-millimeter/laser-based infrared attempt to determine ozone intensities, is unique in that infrared intensities are ultimately anchored to dipole measurements accurate to the 0.1% level. A brief overview of previous ozone studies will be provided along with a detailed description of the experiment configuration and preliminary results.

In this work, a spectrally accurate linelist has been generated for the O₂ Schumann-Runge band system, X³Σ_g⁻ - B³Σ_u⁻, including both the bound-bound and bound-unbound transitions. Ab initio potential energy curves (PECs) for both states and the transition dipole moment (TDM) have been computed using the multi-reference configuration interaction (MRCI) method. Empirical refinement of the potential energy curves along with spin coupling constants have been performed using the DUO software utilizing the O₂ MARVEL database from Furtenbacher et al (J. Phys. Chem. Ref. Data 48, 023101 (2019)). Comparison with room and high temperature cross-sections have also been performed. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

We have investigated collisional broadening and pressure-induced frequency shift for H₂O transitions broadened by O₂. For this, we have obtained one pure and four O₂-mixture spectra of H₂O in the ν₂ region at room temperature using a high-resolution Fourier transform spectrometer (Bruker IFS-125HR) at the Jet Propulsion Laboratory. Using a high-precision spectrum fitting package, Labfit, which adopted non-linear least squares curve fitting algorithm based on a Voigt line shape profile, we have retrieved the two line shape parameters as well as the line positions by fitting all the five spectra simultaneously. It should be noted, however, that their line intensities have been held to the HITRAN values, which improved the precision of the widths and shifts retrieval to a sub% level for most of the transitions. Results from this work have been used to improve the intermolecular potential of the collisional pair, H₂O-O₂, as part of the theoretical model calculations for O₂-broadened H₂O transitions. We will present and discuss the retrieval methodology and the impact of the measurement results on the theoretical model calculations, which are expected to produce more accurate line shape parameters for the entire rovibrational transitions of H₂O in the infrared.Government support acknowledged.html:<hr /><h3>Footnotes: Government support acknowledged.

The second positive system (C³Π_u - B³Π_g) for N₂ has been widely used for optical diagnostics in plasma systems, hypersonic environments, and astrophysics. To this end, a spectrally accurate linelist has been generated for the second positive band system. Ab initio potential energy curves (PECs) and the transition dipole moment (TDM) from Ni and Cheng [1] have been used to calculate new electronic-vibrational transition moments, extending up to v = 29 for the B³Π_g, using the DUO program. Spectral constants from Western et al. [2] and Roux et al. [3] have been compiled along with the new electronic-vibrational transition moments in PGOPHER software to generate the new linelist. Comparisons to experimental data and the SpecAir software have been used to validate the new linelist. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. 1. Ni, C., and Cheng, X. Äb initio study of the second positive system of N₂ at high temperature," Computational and Theoretical Chemistry Vol. 1197, 2021, p. 113158. 2. Western, C. M., Carter-Blatchford, L., Crozet, P., Ross, A. J., Morville, J., and Tokaryk, D. W. "The spectrum of N₂ from 4,500 to 15,700 cm⁻¹ revisited with PGOPHER," Journal of Quantitative Spectroscopy and Radiative Transfer Vol. 219, 2018, pp. 127-141. 3. Roux, F., Michaud, F., and Vervloet, M. "High-resolution Fourier spectrometry of ¹⁴N₂ violet emission spectrum: extensive analysis of the C³Π_u → B³Π_g system," Journal of molecular spectroscopy Vol. 158, No. 2, 1993, pp. 270-277.

While the number of sulfur containing species detected in the interstellar medium has grown in recent years, the detected species still cannot account for the interstellar abundance of sulfur. Thus, in a effort to identify new species that might be of astrochemical interest, an electrical discharge nozzle has been used to generate terrestrially unstable sulfur-bearing species. In our experiment we have paired an electrical DC-discharge nozzle with a broadband microwave spectrometer to measure the resulting products of the discharge of small organic compounds previously identified in the molecular inventory. The rotational spectra from new species are then used for astronomical searches with radio telescopes. Furthermore, we investigate probable reaction pathways that these species could participate in through quantum chemical calculations, providing a global view of the matter cycle in the interstellar medium. In this talk we will present the optimization and benchmarking of our newly-built source as well as some preliminary results on sulfur chemistry and their interpretation.

An ab initio study of the rovibronic spectra of sulphur monoxide (³²S¹⁶O) using internally contracted multireference configuration interaction (ic-MRCI) method using aug-cc-pV5Z basis sets is presented. It covers 13 electronic states X³Σ⁻, a¹∆, b¹Σ⁻, c¹Σ⁻, A^′′3Σ⁺, A^′3∆, A³Π, B³Σ⁻, C³Π, d¹Π, e¹Π, C^′3Π, and (3)¹Π ranging up to 66800 cm⁻¹. The ab initio spectroscopic model includes 13 potential energy curves, 29 dipole and transition dipole moment curves, 25 spin-orbit curves, and 18 electronic angular momentum curves. A diabatic representation is built by removing the avoided crossings between the spatially degenerate pairs C³Π-C^′3Π and e¹Π-(3)¹Π through a property-based diabatisation method. Non-adiabatic couplings and diabatic couplings for these avoided crossing systems are also presented. Finally, a rovibronic spectrum of SO is computed, where an initial refinement of the model to experimental data is shown - producing an initial semi-empirical line list for SO. All phases for our coupling curves are defined, and consistent, providing the first fully reproducible spectroscopic model of SO covering the wavelength range up to 147 nm. We present a diabatisation procedure where the numerical equivalences between the diabatic and adiabatic representations are tested. We show that the commonly ignored first and second order non-adiabatic coupling terms are essential to the equivalence of the two representations, where we provide an analysis on the energy level convergences with basis size for Yitrium Oxide (YO) and a physical set of synthetic potential energy curves in the diabatic and adiabatic representations. The effect of this diabatisation on the accuracy of the final semi-empirical line list of SO is then discussed.

Absolute frequencies of 106 ro-vibrational transitions belonging to the 20012-00001 and 20013-00001 bands of ¹²CO₂ have been measured by saturation spectroscopy. Lamb dips were observed using a cavity ring-down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator. The feed-forward techniqueGotti et al., J Chem Phys 2018, 148, 054202as applied to transfer the coherence of very stable comb emission lines to the laser source of the spectrometer (an external cavity diode laser) via an electro-optic modulator. This setup allows achieving transition frequencies measurements with kHz-level accuracy. The transition frequencies of the two bands are reproduced with a (1σ)-rms of about 1 kHz using the standard expression of the ground and upper energy levels, the ground state constants being constrained to the values reported in Wu et al.Wu et al., Phys Chem Chem Phys, 2020, 22, 2841-2848he 20012 and 20013 vibrational states appear thus to be highly isolated except for a local perturbation of the 20012 state leading to an energy shift of 15 kHz at J'=43. Finally, comparison to transition frequencies reported in the HITRAN2020 database and the literature will be presented and discussed.

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Footnotes:

Gotti et al., J Chem Phys 2018, 148, 054202w Wu et al., Phys Chem Chem Phys, 2020, 22, 2841-2848T