Energy Dissipation and Nonthermal Diffusion on Interstellar Ice Grains
Energy Dissipation and Nonthermal Diffusion on Interstellar Ice Grains
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DOI：
10.3847/1538-4357/aa8c05
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发表时间：
2017-11-10
影响因子：
4.9
通讯作者：
Cuppen, H. M.
中科院分区：
文献类型：
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作者：
Fredon, A.;Lamberts, T.;Cuppen, H. M.
众所周知，星际尘埃颗粒通过充当聚会点和吸附能量来促进化学反应。这一过程在很大程度上取决于反应物质在表面有效扩散的能力。寒冷的气温在10度左右。除H和H-2外，K对其他物种有强烈的抑制作用。然而，在这些寒冷的条件下，在气相中观察到复杂的有机分子，这表明它们的形成以及它们返回气相应该是有效的。在这里，我们展示了表面反应后释放的能量如何通过诱导解吸或扩散来解决这两个问题。为此，我们进行了数千次分子动力学模拟，以量化能量耗散过程的结果。在结晶水面上的Admolecules的平动能在0.5到5之间。电动汽车。考虑了三种不同的表面物质（CO2、H2O和CH4），它们在结合能、内部自由度和分子量上具有一定的范围。研究人员发现，这些加分子在静止之前可以移动几百埃，从而允许在途中进行后续反应。超出任何特定半径的旅行概率，正如我们的模拟所确定的那样，对所有三种admolecule物种都显示出相同的r依赖关系。此外，我们已经能够量化解吸概率，这取决于物种的结合能和平移激发。我们提供了可以纳入天体化学模型的表达式，以预测这些产品的颗粒表面形成和返回气相。
Interstellar dust grains are known to facilitate chemical reactions by acting as a meeting place and adsorbing energy. This process strongly depends on the ability of the reactive species to effectively diffuse over the surface. The cold temperatures around 10. K strongly hamper this for species other than H and H-2. However, complex organic molecules have been observed in the gas phase at these cold conditions, indicating that their formation, as well as their return to the gas phase, should be effective. Here, we show how the energy released following surface reactions can be employed to solve both problems by inducing desorption or diffusion. To this purpose, we have performed thousands of Molecular Dynamics simulations to quantify the outcome of an energy dissipation process. Admolecules on top of a crystalline water surface have been given translational energy between 0.5 and 5. eV. Three different surface species are considered (CO2, H2O, and CH4), spanning a range in binding energies, number of internal degrees of freedom, and molecular weights. The admolecules are found to be able to travel up to several hundreds of angstroms before coming to a stand still, allowing for follow-up reactions en route. The probability of travel beyond any particular radius, as determined by our simulations, shows the same r dependence for all three admolecule species. Furthermore, we have been able to quantify the desorption probability, which depends on the binding energy of the species and the translational excitation. We provide expressions that can be incorporated in astrochemical models to predict grain surface formation and return into the gas phase of these products.