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Paper: Accurate and Consistent Prediction of Molecular IR Line Lists Based on Ab Initio Theory and High-Resolution Experimental Data
Volume: 515, Workshop on Astrophysical Opacities
Page: 155
Authors: Huang, X.; Schwenke, D. W.; Lee, T. J.
Abstract: In the last 10 years, the prediction-oriented “best theory + high-resolution experimental data” strategy has been extended from water to NH3, CO2, and SO2. To compute the molecular infrared (IR) opacity, the accuracy of experimental line positions is combined with the consistency of high-quality ab initio theory. The Ames IR line lists computed on the empirically refined ab initio potential energy surface go beyond the reproduction of existing data to make predictions as accurate as 0.01–0.02 cm-1 for line positions and σ<5–10% for line intensities. They provide valuable reference data and assignments for missing IR bands or minor isotopologues, identify the defects and unreliable extrapolations of existing effective Hamiltonian (EH) models, and improve molecular IR opacity databases. Recent experiments have verified the accuracy, consistency, and completeness of the Ames IR list predictions. Examples are given to demonstrate the EH database deficiencies, experimental difficulties, and the prediction accuracy and consistency of our work. Our latest study has pushed the strategy to a higher level: the microwave spectra of the SO2 minor isotopologues can be predicted with 1–5 MHz accuracy in the range of J<20 and Ka<10–15, and 0.01–0.02 MHz for the rotational constants A0/B0/C0. Ames IR intensity predictions have very high consistency across all isotopologues. These data provide quality control over experimental data or effective dipole moment models, and allow future “refinement” on intensities when much more accurate experimental intensity data become available. See for the latest updates of the Ames molecular IR line lists.
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