Collision-induced absorption (CIA) spectra of nitrogen and methane are needed to model radiative transfer in atmospheres of objects such as Saturn’s moon, Titan. We present Fourier transform infrared spectra of nitrogen and methane rototranslation CIA in the range of 40-600 cm⁻¹. The peak CIA of methane was found to be 7.20*10⁻⁶ cm⁻¹/amagat² at 124.5 K while nitrogen had a peak value of 7.15 *10⁻⁶ cm⁻¹/amagat² at an average temperature of 102.5 K. Work is also underway on the CH₄-N₂ CIA system.

Gas giant planets are predominantly composed of H₂, and H₂-H₂ collision-induced absorption (CIA) is the major source of their atmospheric opacity below 800 cm⁻¹and also plays a significant role near 1200 cm⁻¹as well. Interpretation of satellite and ground-based planetary spectra relies on the widely accepted Borysow CIA model calculations. It has long been noted that planetary spectra above 600 cm⁻¹are not well matched using this CIA model. Thus we conducted a laboratory study to measure the CIA of H₂-H₂ in the broad spectral region at the AILES beamline, Synchrotron Soleil, France. We obtained a series of spectra of pure H₂ at various pressures and temperatures in the range 112 - 118 K using the multi-reflection absorption cell coupled to a Fourier-transform spectrometer. Details of the experimental procedure and preliminary results are presented. The measurement uncertainty is discussed, and a comparison of these results to the Borysow model of H₂ CIA will be presented.Government sponsorship acknowledgedhtml:<hr /><h3>Footnotes: Government sponsorship acknowledged

The James Webb Space Telescope has transformed our understanding of exoplanet atmospheres, revealing unidentified spectral lines whose molecular origins could challenge existing models of exoplanet chemistry, physics, geology, and potentially biology. Our role as spectroscopists is to help astronomers decipher these unexpected signals. To achieve secure detections, constructing high-accuracy line lists for specific molecules at elevated temperatures typically requires years of experimental and theoretical effort. However, an essential initial step is to shortlist candidate molecules responsible for these unknown lines. Our innovative high-throughput computational approach provides approximate fundamental vibrational band centers and intensities, along with error estimates, for nearly 2000 molecules containing up to 6 non-hydrogen atoms. This methodology can be extended to generate data for any plausible non-metal gaseous molecule. We are also developing techniques for approximate cross-sections at different temperatures using rotational constants, anharmonic approaches for overtone and combination bands, and methods to model vibrational hot bands. Benchmarking is crucial in all theoretical approaches to provide reasonable error estimates. With our dataset of approximate spectral data with estimated errors, we can identify a shortlist of molecular candidates for each unknown band. This list can be evaluated through manual literature searches for additional experimental data and targeted, very high accuracy quantum chemistry calculations. Our initial tests show that many candidate molecules are chemically unconventional and unlikely to be present. Incorporating a more data-driven and semi-automated estimation of molecular abundance in certain atmosphere classes would enhance our approach. The dataset's size prompts consideration of using machine learning to explore a larger set of molecules, particularly bigger ones relevant in cooler gaseous environments like solar system moons. I will briefly present preliminary results highlighting the importance of data quality in ensuring the accuracy of machine learning models. Model evaluation should be based on experimental data rather than computationally-generated training data. Molecular similarity analysis can also assist in predicting the uncertainty of predictions for new molecules.

For those IR line lists semi-empirically computed for polyatomic molecules using their potential energy surfaces (PES) refined with high-resolution experimental data, their line position accuracy typically falls within 0.01 - 0.05 cm⁻¹. It is preferable to enhance these line lists with more accurate line positions derived from experiments and/or Effective Hamiltonian models. However, this task is not straightforward and heavily relies on the specific molecule, mainly contingent upon the consistency and accuracy of the data available. Recently, we have tried to improve the Ames-296K IR line listhttps://huang.seti.org/OCS/ocs.htmlor carbonyl sulfide (σ_rms=0.007 cm⁻¹) by utilizing HITRAN data (for 6 isotopologues), MARVEL level set (for the primary isotopologue 622)Even Xu & Jonathan Tennyson (2023) Mol. Phys, e2279694 and high-resolution experiments. In order to minimize the impact of various inconsistencies, less accurate data, and even errors identified in the data, we opted to implement state-specific adjustments on Effective Hamiltonian model-based levels and the original rovibrational levels computed variationally on the Ames-1 PES refinement. In this talk, we will present our discoveries ranging from better-than-expected agreements to enlightening discrepancies, explain the reasoning and intricacies behind the adjustments, and discuss remaining issues and future enhancements. It is worth noting that matching to a global Effective Hamiltonian model (when available) would be a distinct and more challenging scenario. The new Ames-296K OCS line list includes an estimate of uncertainty for each updated line position.

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Footnotes:

https://huang.seti.org/OCS/ocs.htmlf Even Xu & Jonathan Tennyson (2023) Mol. Phys, e2279694,

The atmosphere of Venus is primarily composed of CO₂ (96.5%), N₂ ( ∼ 3.5%), Ar (0.01%), and trace amounts of other chemical compounds. Although CO₂ is supposed to be dissociated to CO and O₂ by solar ultraviolet radiation, an enormous amount of CO₂ still exists in Venus's atmosphere. In the CO₂ cycle, the ClCO and ClC(O)OO are critical in the reactions, being the intermediates in the reactions.W. B. DeMore, Yuk L. Yung, Catalytic Processes in the Atmospheres of Earth and Venus. Science, 217, 1209-1213 (1982)he pure rotational transitions of ClCO and ClC(O)OO were measured using Fourier transform microwave spectroscopy in the region of 8 GHz to 40 GHz. In the case of ClCO, both the isotopologues ³⁵ClCO and ³⁷ClCO were observed, while only a-type transitions with K_a = 0 were observed due to the fairly large rotational constant A. When it comes to ClC(O)OO, which was expected to be produced from the reaction of ClCO and O₂, both cis-ClC(O)OO and trans-ClC(O)OO were observed. Fine and hyperfine components of both conformers were well-assigned, leading to the precisely determined fine and hyperfine constants. The trans-ClC(O)OO radical is a prolate asymmetric top molecule with rotational constants A > B ≈ C, while the cis-ClC(O)OO is more like an oblate top molecule with rotational constants A ≈ B > C. The unpaired electrons on both ClC(O)OO conformers are mainly on out-of-plane π orbitals of the terminal oxygens of the COO moiety. Moreover, due to the position of the unpaired electron, the hyperfine coupling constants of chlorine are very small.

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Footnotes:

W. B. DeMore, Yuk L. Yung, Catalytic Processes in the Atmospheres of Earth and Venus. Science, 217, 1209-1213 (1982)T

This presentation is centered on introducing an innovative experimental platform dedicated to the study of ion-neutral collisions, with a special emphasis on molecules present in the interstellar medium (ISM). Our goal is to accurately replicate the ISM environment in a laboratory setting, focusing on a broad energy spectrum that ranges from 10 to 5000 K and ensuring high collision energy resolution of < 10 K. The key feature of the new method is the precise control of ion velocities, enabling studies of collisions across a wide range of energies with high resolution. Experimental design, calculations, and preliminary results will be presented in this talk.

Infrared gas phase spectroscopy has a long and rich history of providing detailed information on the structure and behavior of molecules. Recently, the need to develop new techniques has been motivated by pressing problems such as climate change and exciting new opportunities such as the ability to determine the atmospheric composition of exoplanets. These kinds of applications can present challenges for existing 1D spectroscopic methods such as spectral congestion at high temperatures. This talk describes how 2DRV spectroscopy can provide solutions to some of these challenges. 2DRV spectra contain multidimensional patterns with detailed information about molecular structure and behavior for molecules at elevated temperatures. It can also use assignments in less congested lower frequency regions to make new assignments in more congested higher frequency regions. This talk will describe the kinds of patterns that are formed, new methods for creating and analyzing them, and what we can learn from them.

Two dimensional (2D) spectroscopy is a technique that can be used to identify vibrational couplings between two regions of the IR spectrum. This technique is well-established for molecules in condensed phases. A recently demonstrated technique, 2D rovibrational spectroscopy of gas phase molecules, introduces new possibilities because numerous rovibrational peaks can form unique and informative patterns. This talk presents 2D spectra of monodeuterated methane (CH3D) that show rovibrational patterns created by couplings between vibrations in the NIR and MIR regions. New 2D methods of analysis lead to assignments in the MIR and NIR region and greater understanding of the molecule’s behavior.

This project involves the use of a new technique, Two-dimensional Rovibrational spectroscopy (2DRV), for studying the complex spectroscopy of gas phase molecules such as ammonia. 2DRV has been used to record spectra of a handful of molecules, including methane, propyne, chloromethane, and dichloromethane. The 2DRV spectra of ammonia are especially interesting because of the molecule’s large-amplitude umbrella motion and the importance of ammonia in the atmosphere. These spectra also show which vibrational modes are coupled. New 2D analysis techniques provide unique ways of assigning peaks by their vibrational and rotational quantum numbers, and those assignments can be compared with those currently in the HITRAN database.