Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P4O6) Have Significant Implications for Phosphorus Species in Planetary Atmospheres,ACS Earth and Space Chemistry

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Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P4O6) Have Significant Implications for Phosphorus Species in Planetary Atmospheres
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2023-05-22 , DOI: 10.1021/acsearthspacechem.3c00016
William Bains _{1,

2,

3} , Matthew A. Pasek ₄ , Sukrit Ranjan ₅ , Janusz J. Petkowski _{1,

6} , Arthur Omran ₄ , Sara Seager _{1,

7,

8}

Affiliation

Phosphorus (III) oxide (P₄O₆) has been suggested to be a major component of the gas phase phosphorus chemistry in the atmospheres of gas giant planets and of Venus. However, P₄O₆’s proposed role is based on thermodynamic modeling, itself based on values for the free energy of formation of P₄O₆ estimated from limited experimental data. Values of the standard Gibbs free energy of formation (ΔG^o_(g)) of P₄O₆ in the literature differ by up to ∼656 kJ/mol, a huge range. Depending on which value is assumed, P₄O₆ may either be the majority phosphorus species present or be completely absent from modeled atmospheres. Here, we critically review the literature thermodynamic values and compare their predictions to observed constraints on P₄O₆ geochemistry. We conclude that the widely used values from the NIST/JANAF database are almost certainly too low (predicting that P₄O₆ is more stable than is plausible). We show that, regardless of the value of ΔG^o_(g) for P₄O₆ assumed, the formation of phosphine from P₄O₆ in the Venusian atmosphere is thermodynamically unfavorable. We conclude that there is a need for more robust data on both the thermodynamics of phosphorus chemistry for astronomical and geological modeling in general and for understanding the atmosphere of Venus and the gas giant planets in particular.

中文翻译：

氧化磷 (III) (P4O6) 热力学的巨大不确定性对行星大气中的磷物质具有重大影响

氧化磷（III）（P ₄ O ₆）被认为是气态巨行星和金星大气中气相磷化学的主要成分。然而，P ₄ O ₆的提议作用是基于热力学模型，其本身基于根据有限的实验数据估计的 P ₄ O ₆形成自由能的值。文献中P ₄ O ₆的标准吉布斯生成自由能(ΔG o (g) ) 的值相差^高达_∼656 kJ/mol，范围很大。根据假设的值，P ₄ O ₆可能是模拟大气中存在的主要磷物质，也可能完全不存在。在这里，我们批判性地回顾了文献热力学值，并将其预测与观察到的 P ₄ O ₆地球化学约束进行了比较。我们得出的结论是，NIST/JANAF 数据库中广泛使用的值几乎肯定太低（预测 P ₄ O ₆比看似合理的更稳定）。^我们表明，无论假定P ₄ O _{6的 Δ}Go _(g)值如何，P ₄ O ₆都会形成磷化氢金星大气层中的空气在热力学上是不利的。我们的结论是，一般天文和地质建模以及了解金星和气态巨行星的大气层都需要更可靠的磷化学热力学数据。

更新日期：2023-05-22

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