Nowadays exoplanet atmospheric modeling is focused primarily on giant exoplanets close to their host stars due to their easier detection and characterization by direct imaging. However, the introduction of James Webb Space Telescope (JWST) will enable us to obtain high-quality spectra of exoplanet atmospheres of various sizes and distances from their host star, including low-temperature conditions similar to that of our outer planetary system (e.g., Titan). Reliable interpretation of such spectra will require complex self-consistent photochemical models for which accurate reaction rate coefficients are indispensable. Unfortunately, low-temperature reaction rate coefficients relevant to cool rocky exoplanet atmospheres are currently not well-constrained due to the extreme difficulty in measuring them accurately in the lab. An alternate approach is to employ a high-level ab initio quantum chemical method to calculate such low-temperature reaction rate coefficients. We are using this approach to investigate some key radical–radical and radical–neutral reactions that directly impact the production/loss of chemical species such as NH3, HCN, H2O, CO, CO2, C3H8, etc. The versatility of our theoretical method enables us to study chemical reactions of modestly sized molecules (i.e., less than 40 electrons to keep the computational cost within reach) for any gaseous environment (e.g., H2, He, N2, NH3, CH4, CO2, O2, NOx, SOx, etc.). In addition, our method covers a wide range of temperatures (10–300K) and pressures (microbar to bars). Our calculated rate coefficients will be made available to the public via established databases and repositories like Planetary Data System Atmospheres (PDS ATM), Kinetic Database for Astrochemistry (KIDA), Exoplanet Modeling and Analysis Center (EMAC), etc. Modelers can use our rate coefficient data to develop accurate atmospheric photochemical models for cool rocky exoplanets that are to be detected/characterized in the near future by JWST.

Improving atmospheric photochemical models for cool rocky exoplanets with new low-temperature reaction rate coefficients

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.