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Rovibrational Collisional Excitation of Diatomic and Triatomic Molecules by Quantum Computations and Machine Learning for Modeling of Infrared Observations, Phillip Stancil

Refractory elements are deemed to be incorporated into interstellar dust grains, but their observed presents in the gas-phase suggests the grains reside in turbulent environments, e.g. intense ultraviolet radiation fields or high-velocity shocks. To aid in the understanding of observations of refractory molecules, we propose to compute accurate collisional excitation rate coefficients for rotational and vibrational transitions of NaCl, AlCl, AlO, SiS, SH, and H2S due to H and H2 impact. This work, which uses fully quantum mechanical methods for inelastic scattering and incorporates full-dimensional potential energy surfaces (PESs), pushes beyond the state-of-the-art for such calculations, as recently established by our group for rovibrational transitions in full-dimension. All the required PESs will be computed as part of this project using ab initio theory and basis sets of the highest level feasible and particular attention will be given to the long range form of the PESs. The completion of the project will result in 12 new interaction PESs. The state-to-state rate coefficients for a large range of initial rovibrational levels for temperatures between 1 and 3000 K will be computed and extended to higher excitation using artificial neural network and gaussian process regression approaches. The chosen collision systems correspond to cases where data are limited or lacking, include less-studied refractory elements, and will provide observable emission/absorption features in the infrared (IR). The final project results will be important for the analysis of a variety of interstellar and extragalactic environments in which the local conditions of gas density, radiation field, and/or shocks drive the level populations out of equilibrium. In such cases, collisional excitation data are critical to the accurate prediction and interpretation of observed molecular IR emission lines in protoplanetary disks, star-forming regions, planetary nebulae, embedded protostars, and photodissociation regions. The use of the proposed collisional excitation data will lead to deeper examination and understanding of the properties of many astrophysical environments, hence elevating the scientific return from the soon-to-be-launched JWST, as well as from current (SOFIA, HST) and past IR missions (Herschel, Spitzer, ISO), and from ground-based telescopes.

  • Funder: National Aeronautics and Space Administration (NASA)
  • Amount: $911,454
  • PI: Phillip Stancil