On Simulating the Proton-irradiation of O2 and H2O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity
On Simulating the Proton-irradiation of O2 and H2O Ices Using Astrochemical-type Models, with Implications for Bulk Reactivity
复制标题
使用天体化学类型模型模拟 O2 和 H2O 冰的质子辐照，并对本体反应性产生影响
DOI：
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发表时间：
2019
影响因子：
4.9
通讯作者：
P. Caselli
中科院分区：
文献类型：
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作者：
C. Shingledecker;A. Vasyunin;E. Herbst;P. Caselli
许多目前的天体化学模型明确地考虑了构成大部分星际尘埃颗粒冰盖的物种，而不是那些位于最上面几个单层的物种。通过电离辐射轰击这些冰--无论是以宇宙射线、恒星风或放射性核素发射的形式--代表了一种在天体化学上可行的方法，即使在冰地幔的大部分也可以驱动丰富的化学物质，现在实验室天体物理学的大量工作支持这种方法。在这项研究中，我们尝试用现有的基于速率方程的天体化学程序来模拟两个这样的研究：(A)在5K下纯O2冰和在16K和77K下纯H2O冰被KeV H+离子轰击。我们的目标有两个：(1)测试我们新开发的方法复制冰辐照实验结果的能力，以及(2)确定如何使用用于模拟星际介质的相同气体-颗粒代码来处理如此严格限制的系统中的主体化学。我们发现，我们改进的天体化学模型能够再现5K纯氧冰中臭氧的丰度，以及16K水冰中过氧化氢的丰度，以及先前提到的更高温度下过氧化氢的减少。然而，这些结果需要假设通过辐射分解产生的自由基和其他活性物种与冰中的邻居快速且非扩散地反应。
Many current astrochemical models explicitly consider the species that comprise the bulk of interstellar dust grain ice mantles separately from those in the top few monolayers. Bombardment of these ices by ionizing radiation—whether in the form of cosmic rays, stellar winds, or radionuclide emission—represents an astrochemically viable means of driving a rich chemistry even in the bulk of the ice mantle, now supported by a large body of work in laboratory astrophysics. In this study, using an existing rate-equation-based astrochemical code modified to include a method of considering radiation chemistry recently developed by us, we attempted to simulate two such studies in which (a) pure O2 ice at 5 K and (b) pure H2O ice at 16 K and 77 K, were bombarded by keV H+ ions. Our aims were twofold: (1) to test the capability of our newly developed method to replicate the results of ice-irradiation experiments, and (2) to determine how bulk chemistry in such a well-constrained system is best handled using the same gas-grain codes that are used to model the interstellar medium. We found that our modified astrochemical model was able to reproduce both the abundance of O3 in the 5 K pure O2 ice, as well as both the abundance of H2O2 in the 16 K water ice and the previously noted decrease of hydrogen peroxide at higher temperatures. However, these results require the assumption that radicals and other reactive species produced via radiolysis react quickly and non-diffusively with neighbors in the ice.