CDS&E: Mixed Quantum/Classical Theory for the Collisional Quenching of Interstellar Complex Organic Molecules

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Dmitri Babikov of Marquette University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry to predict the collisional quenching rates of several molecules important for astrochemical applications. These data, obtained for the relevant broad range of temperatures, will be delivered to the scientific community at large, and especially to astronomers, by means of publishing these data in the database BASECOL. Being incorporated into the radiation transfer codes presently in use in the astrophysics community, this information will enable astronomers to quantify the abundance of these molecules in pre-stellar cores and proto-stellar jets. The standard quantum calculations of rotationally inelastic collisions become prohibitively demanding at higher collision energies and for heavier molecules, such as the interstellar complex organic molecules (iCOMs). To overcome this obstacle, it is proposed to develop a practical computational treatment of scattering where the relative motion of collision partners is described classically, while their internal degrees of freedom (rotation, vibration) are still described quantum mechanically. This approach is expected to be both accurate and computationally affordable. For the successful quantitative interpretation of astrophysical observations it is imperative to know cross sections for collisional state-to-state excitation/quenching of the light-emitting molecules by typical background gasses, such as He and H2, across a broad range of temperatures. This information, however, is largely unavailable and there is no simple way of obtaining this from experiments. Dmitri Babikov is developing a mixed quantum/classical theory (MQCT) and a user-friendly suite of programs for efficient simulations of inelastic molecular collisions, capturing the effects of scattering phase important for differential cross-sections, translational-to-internal resonant energy transfer and revealing the role of PES anisotropy. In this project MQCT calculations of inelastic scattering will be carried out for several SOLIS molecules (seeds of life in space: includes methanol (CH3OH), methyl formate (HCOOCH3(, dimethyl ether (CH3OCH3(, acetaldehyde (CH3COH) and formamide (H2NCOH), colliding with He and H2 in temperature ranges that are typically found in solar-like proto-stars, and in interstellar and circumstellar environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.