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Nature and evolution of the dominant carbonaceous matter in interplanetary dust particles: effects of irradiation and identification with a type of amorphous carbon

机译:行星际尘埃颗粒中主要碳质物质的性质和演化:辐射的影响和一种无定形碳的识别

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摘要

Aims.Interplanetary dust particle (IDP) matter probably evolved under irradiation in the interstellar medium (ISM) and the solar nebula. Currently IDPs are exposed to irradiation in the Solar System. Here the effects of UV and proton processing on IDP matter are studied experimentally. The structure and chemical composition of the bulk of carbon matter in IDPs is characterized. Methods: .Several IDPs were further irradiated in the laboratory using ultraviolet (UV) photons and protons in order to study the effects of such processing. By means of infrared and Raman spectroscopy, IDPs were also compared to different materials that serve as analogs of carbon grains in the dense and diffuse ISM. Results: .The carbonaceous fraction of IDPs is dehydrogenated by exposure to hard UV photons or 1 MeV protons. On the other hand, proton irradiation at lower energies (20 keV) leads to an efficient hydrogenation of the carbonaceous IDP matter. The dominant type of carbon in IDPs, observed with Raman and infrared spectroscopy, is found to be either a form of amorphous carbon (a-C) or hydrogenated amorphous carbon (a-C:H), depending on the IDP, consisting of aromatic units with an average domain size of 1.35 nm (5-6 rings in diameter), linked by aliphatic chains. Conclusions: .The D- and 15N-enrichments associated to an aliphatic component in some IDPs are probably the result of chemical reactions at cold temperatures. It is proposed that the amorphous carbon in IDPs was formed by energetic processing (UV photons and cosmic rays) of icy grains, maybe during the dense cloud stage, and more likely on the surface of the disk during the T Tauri phase of our Sun. This would explain the isotopic anomalies and morphology of IDPs. Partial annealing, 300-400°C, is required to convert an organic residue from ice photoprocessing into the amorphous carbon with low heteroatom content found in IDPs. Such annealing might have occurred as the particles approached the Sun and/or during atmospheric entry heating.
机译:目的:星际尘埃粒子(IDP)物质可能是在星际介质(ISM)和太阳星云的辐射下演化而来的。当前,国内流离失所者受到太阳系的辐射。在这里,实验研究了紫外线和质子处理对IDP物质的影响。对IDP中大部分碳物质的结构和化学成分进行了表征。方法:。在实验室中进一步使用紫外线(UV)光子和质子辐照几个IDP,以研究这种处理的效果。通过红外光谱和拉曼光谱,还将IDP与不同的材料进行了比较,这些材料在密集和分散的ISM中用作碳粒的类似物。结果:通过暴露于硬紫外线光子或1 MeV质子,IDPs的碳级分被脱氢。另一方面,在较低能量(20 keV)下进行质子辐照可导致碳质IDP物质高效氢化。通过拉曼光谱和红外光谱观察,发现IDP中的主要碳类型为无定形碳(aC)或氢化无定形碳(aC:H)的形式,具体取决于IDP,由平均芳香族单元组成域大小为1.35 nm(直径5-6环),由脂肪链连接。结论:在某些IDP中,与脂肪族成分相关的D和15N富集可能是低温下化学反应的结果。有人提出,IDPs中的无定形碳是由冰粒的高能处理(紫外线光子和宇宙射线)形成的,可能是在浓云阶段,而更可能是在太阳的T Tauri相期间在磁盘表面上形成的。这将解释IDP的同位素异常和形态。需要进行300-400°C的部分退火,以将冰光处理中的有机残留物转化为IDP中低杂原子含量的无定形碳。当颗粒接近太阳时和/或在大气进入加热期间,可能已经发生了这种退火。

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