多孔颗粒表面化学的多层模拟I。GRAINOBLE模型
Multilayer modeling of porous grain surface chemistry I. The GRAINOBLE model
摘要：
冰水的地幔，与CO，H2CO和CH3OH混合，在所谓的星前核心阶段形成。此外，自由基也被认为是在颗粒表面形成的，并在后来的原恒星演化的升温阶段反应形成复杂的有机分子。我们的目的是研究形成的粮食地幔在星前核心阶段和丰富的H2CO，CH3OH，和自由基被困在他们。我们开发了一个宏观统计多层模型，该模型遵循随时间形成的颗粒地幔，并且包括可能增加被困在地幔中的自由基数量的两种效应：i）在地幔形成的每个时间，只有表面层是化学活性的，而不是整个主体，以及ii）颗粒的多孔结构允许捕获反应性颗粒。该模型考虑了H、O和CO形成的中性物质（例如水、CO、甲醛和甲醇）以及几个自由基的网络。我们运行了一个大型网格模型来研究地幔多层性质和颗粒多孔结构的影响。此外，我们还探讨了其他关键参数的不确定性对地幔成分的影响。我们的模型预测相对较大丰度的自由基。此外，多层的方法使得它有可能遵循的化学分异内的粮食地幔，表明地幔是远远不是均匀的。例如，甲醇主要存在于地幔的外层，而CO和其他活性物质则被困在内层。整个地幔的组成取决于星前核的密度和年龄，以及一些微观参数。与观测结果的比较使我们能够限制一些参数的值，并提供一些指示的物理条件在冰的形成。
英文摘要：
Mantles of iced water, mixed with CO, H2CO, and CH3OH are formed during the so called prestellar core phase. In addition, radicals are also thought to be formed on the grain surfaces, and to react to form complex organic molecules later on, during the warm-up phase of the protostellar evolution. We aim to study the formation of the grain mantles during the prestellar core phase and the abundance of H2CO, CH3OH, and radicals trapped in them. We have developed a macrosopic statistic multilayer model that follows the formation of grain mantles with time and that includes two effects that may increase the number of radicals trapped in the mantles: i) at each time of the mantle formation, only the surface layer is chemically active rather than the entire bulk, and ii) the porous structure of grains allows to trap reactive particles. The model considers a network of H, O and CO forming neutral species such as water, CO, formaldehyde, and methanol, plus several radicals. We run a large grid of models to study the impact of the mantle multilayer nature and grain porous structure. In addition, we explored the influence of the uncertainty of other key parameters on the mantle composition. Our model predicts relatively large abundances of radicals. In addition, the multilayer approach makes it possible to follow the chemical differentiation within the grain mantle, showing that the mantles are far from being uniform. For example, methanol is mostly present in the outer layers of the mantles whereas CO and other reactive species are trapped in the inner layers. The overall mantle composition depends on the density and age of the prestellar core, and on some microscopic parameters. Comparison with observations allows us to constrain the value of few parameters and provide some indications on the physical conditions during the formation of the ices.
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