ATMOSPHERIC CHEMISTRY for ASTROPHYSICISTS

A SELF-CONSISTENT FORMALISM and ANALYTICAL SOLUTIONS for ARBITRARY C/O

Kevin Heng, James Lyons, Shang Min Tsai

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

We present a self-consistent formalism for computing and understanding the atmospheric chemistry of exoplanets from the viewpoint of an astrophysicist. Starting from the first law of thermodynamics, we demonstrate that the van't Hoff equation (which describes the equilibrium constant), Arrhenius equation (which describes the rate coefficients), and procedures associated with the Gibbs free energy (minimization, rescaling) have a common physical and mathematical origin. We address an ambiguity associated with the equilibrium constant, which is used to relate the forward and reverse rate coefficients, and restate its two definitions. By necessity, one of the equilibrium constants must be dimensionless and equate to an exponential function involving the Gibbs free energy, while the other is a ratio of rate coefficients and must therefore possess physical units. We demonstrate that the Arrhenius equation takes on a functional form that is more general than previously stated without recourse to tagging on ad hoc functional forms. Finally, we derive analytical models of chemical systems, in equilibrium, with carbon, hydrogen, and oxygen. We include acetylene and are able to reproduce several key trends, versus temperature and carbon-to-oxygen ratio, published in the literature. The rich variety of behavior that mixing ratios exhibit as a function of the carbon-to-oxygen ratio is merely the outcome of stoichiometric book-keeping and not the direct consequence of temperature or pressure variations.

Original languageEnglish (US)
Article number96
JournalAstrophysical Journal
Volume816
Issue number2
DOIs
StatePublished - Jan 10 2016

Fingerprint

formalism
Gibbs free energy
oxygen
carbon
coefficients
atmospheric chemistry
tagging
exponential functions
acetylene
extrasolar planets
mixing ratios
trucks
mixing ratio
ambiguity
marking
thermodynamics
temperature
hydrogen
trends
optimization

Keywords

  • methods: analytical
  • planets and satellites: atmospheres

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

ATMOSPHERIC CHEMISTRY for ASTROPHYSICISTS : A SELF-CONSISTENT FORMALISM and ANALYTICAL SOLUTIONS for ARBITRARY C/O. / Heng, Kevin; Lyons, James; Tsai, Shang Min.

In: Astrophysical Journal, Vol. 816, No. 2, 96, 10.01.2016.

Research output: Contribution to journalArticle

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