Dobrijevic M, Parisot J P, Dutour I
Observatoire de Bordeaux, Floirac, France.
Planet Space Sci. 1995 Jan-Feb;43(1-2):15-24. doi: 10.1016/0032-0633(94)00147-j.
Photochemistry of giant planets and their satellites is characterized by numerous reactions involving many chemical species. In the present paper, chemical systems are modeled by signal flow graphs. Such a technique evaluates the transmission of any input into the system (solar flux, electrons...) and gives access to the identification of the most important mechanisms in the chemical system. For a given chemical system, we first evaluate rate coefficients. Then, in order to obtain concentrations of each compound, we integrate the set of continuity equations by Gear's method. Gear's method is chosen rather than another classical method because it is recommended for a system of stiff equations due to the existence of greatly differing time constants. Finally, the technique of signal flow graphs is used. This method is applied to the production of hydrocarbons in the atmospheres of giant planets. In particular, the production of C2H6 in the atmosphere of Neptune from the photodissociation of CH4 is investigated. Different paths of dissociation of CH4 are possible from L alpha radiations. A chemical system containing 14 species and 30 reactions including these different paths of dissociation is integrated. The main mechanism of production of C2H6 is identified and evaluated for each model of dissociation. The importance of various reaction paths as a function of time is discussed.
巨行星及其卫星的光化学具有众多涉及多种化学物种的反应。在本文中，化学系统由信号流图建模。这种技术评估任何输入进入系统（太阳通量、电子等）的传输，并能够识别化学系统中最重要的机制。对于给定的化学系统，我们首先评估速率系数。然后，为了获得每种化合物的浓度，我们用吉尔方法对连续性方程组进行积分。选择吉尔方法而非其他经典方法，是因为由于存在差异极大的时间常数，对于刚性方程组系统它是推荐方法。最后，使用信号流图技术。该方法应用于巨行星大气中碳氢化合物的生成。特别地，研究了海王星大气中由甲烷光解产生乙烷的过程。从Lα辐射来看，甲烷有不同的解离路径。对包含14种物质和30个反应（包括这些不同解离路径）的化学系统进行了积分。针对每种解离模型确定并评估了乙烷生成的主要机制。讨论了各种反应路径随时间变化的重要性。
