CRAHCN-O: A Consistent Reduced Atmospheric Hybrid Chemical Network Oxygen Extension for Hydrogen Cyanide and Formaldehyde Chemistry in CO₂-, N₂-, H₂O-, CH₄-, and H₂-Dominated Atmospheres

Hydrogen cyanide (HCN) and formaldehyde (H₂CO) are key precursors to biomolecules such as nucleobases and amino acids in planetary atmospheres. However, many reactions which produce and destroy these species in atmospheres containing CO₂ and H₂O are still missing from the literature. We use a quantum chemistry approach to find these missing reactions and calculate their rate coefficients using canonical variational transition state theory and Rice-Ramsperger-Kassel-Marcus/master equation theory at the BHandHLYP/aug-cc-pVDZ level of theory. We calculate the rate coefficients for 126 total reactions and validate our calculations by comparing with experimental data in the 39% of available cases. Our calculated rate coefficients are most frequently within a factor of 2 of experimental values and generally always within an order of magnitude of these values. We discover 45 previously unknown reactions and identify 6 from this list that are most likely to dominate H₂CO and HCN production and destruction in planetary atmospheres. We highlight ¹O + CH₃ → H₂CO + H as a new key source and H₂CO + ¹O → HCO + OH as a new key sink, for H₂CO in upper planetary atmospheres. In this effort, we develop an oxygen extension to our consistent reduced atmospheric hybrid chemical network (CRAHCN-O), building off our previously developed network for HCN production in N₂-, CH₄-, and H₂-dominated atmospheres (CRAHCN). This extension can be used to simulate both HCN and H₂CO production in atmospheres dominated by any of CO₂, N₂, H₂O, CH₄, and H₂.