CO2 formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel
CO2 formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel
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星际尘埃颗粒上 CO2 的形成：CO O 通道势垒的详细研究
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
F. Dulieu
中科院分区：
文献类型：
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作者：
M. Minissale;E. Congiu;G. Manicò;V. Pirronello;F. Dulieu
上下文。尽管二氧化碳是星际冰中最丰富的种类之一，但在分子云的静止区域中二氧化碳的形成还没有被完全理解。目标。在接近静止分子云的条件下，通过在冷表面上氧化CO分子来研究CO2的形成。方法。一氧化碳和氧原子在两个不同的表面（无定形水冰或氧化石墨）在给定的温度在10到60 K之间共沉积使用两个差分抽运光束线。采用程序升温解吸技术对产物进行质谱检测。结果。我们证明了CO + O反应可以在固相中形成二氧化碳，其效率取决于表面温度。根据模拟结果，该反应的激活势垒估计在780 ~ 475 K/kb之间。我们的模型还允许我们区分在不同温度下起作用的机制（Eley Rideal或Langmuir-Hinshelwood）。我们的研究结果表明，通过CO + O和其他O的表面反应生成CO2之间的竞争是实验得到的CO2产率的关键因素。结论。CO + O反应可以通过模拟星际介质中二氧化碳形成的过程在寒冷的表面上形成二氧化碳。从天体物理学的角度来看，静止分子云中二氧化碳的存在可以用发生在星际尘埃颗粒上的CO + O反应来解释。
Context. The formation of carbon dioxide in quiescent regions of molecular clouds has not yet been fully understood, even though CO2 is one of the most abundant species in interstellar ices. Aims. CO2 formation is studied via oxidation of CO molecules on cold surfaces under conditions close to those encountered in quiescent molecular clouds. Methods. Carbon monoxide and oxygen atoms are codeposited using two differentially pumped beam lines on two different surfaces (amorphous water ice or oxydized graphite) held at given temperatures between 10 and 60 K. The products are probed via mass spectroscopy by using the temperature-programmed desorption technique. Results. We show that the reaction CO + O can form carbon dioxide in solid phase with an efficiency that depends on the temperature of the surface. The activation barrier for the reaction, based on modelling results, is estimated to be in the range of 780−475 K/kb .O ur model also allows us to distinguish the mechanisms (Eley Rideal or Langmuir-Hinshelwood) at play in different temperature regimes. Our results suggest that competition between CO2 formation via CO + O and other surface reactions of O is a key factor in the yields of CO2 obtained experimentally. Conclusions. CO2 can be formed by the CO + O reaction on cold surfaces via processes that mimic carbon dioxide formation in the interstellar medium. Astrophysically, the presence of CO2 in quiescent molecular clouds could be explained by the reaction CO + O occurring on interstellar dust grains.