2016/03/31 by Kevin Heng, Shang-Min Tsai · 2 citations
Physics and Astronomy · #Acetylene #Astrochemistry #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Carbon fibers #Carbon monoxide #Chemical equilibrium #Hydrogen #Methane #Molecule #Nitrogen #Stellar, planetary, and galactic studies #astro-ph.EP #physics.ao-ph #physics.chem-ph
paper · pdf · doi:10.3847/0004-637x/829/2/104
Accepted by ApJ. 7 pages, 4 figures
openalex created_date 2016/06/24 · arxiv created 2016/07/15 · openalex publication_date 2016/09/27 · arxiv updated 2016/10/05 · openalex updated_date 2026/08/06
ABSTRACT We present novel, analytical, equilibrium-chemistry formulae for the abundances of molecules in hot exoplanetary atmospheres that include the carbon, oxygen, and nitrogen networks. Our hydrogen-dominated solutions involve acetylene (C 2 H 2 ), ammonia (NH 3 ), carbon dioxide (CO 2 ), carbon monoxide (CO), ethylene (C 2 H 4 ), hydrogen cyanide (HCN), methane (CH 4 ), molecular nitrogen (N 2 ), and water (H 2 O). By considering only the gas phase, we prove that the mixing ratio of carbon monoxide is governed by a decic equation (polynomial equation of 10 degrees). We validate our solutions against numerical calculations of equilibrium chemistry that perform Gibbs free energy minimization and demonstrate that they are accurate at the level for temperatures from 500 to 3000 K. In hydrogen-dominated atmospheres, the ratio of abundances of HCN to CH 4 is nearly constant across a wide range of carbon-to-oxygen ratios, which makes it a robust diagnostic of the metallicity in the gas phase. Our validated formulae allow for the convenient benchmarking of chemical kinetics codes and provide an efficient way of enforcing chemical equilibrium in atmospheric retrieval calculations.