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arXiv 2401.04024astro-ph.GAastro-ph.SR
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在致密云内部相关温度下,含H2、富CO星际冰层中的有机化学

Organic chemistry in the H2-bearing, CO-rich interstellar ice layer at temperatures relevant to dense cloud interiors

Rafael Martín-Doménech, Alexander DelFranco, Karin I. Öberg, Mahesh Rajappan

AI总结:

本研究通过在4-15 K下用2 keV电子辐照CO:15N2:H2冰样品,发现富CO星际冰层中困住的H2分子在能量处理下能生成甲醛、乙烯酮等复杂有机分子,为ISM最冷区域的COMs形成提供了额外贡献。

摘要:

致密、寒冷星际介质(ISM)中的冰化学可能是星际复杂有机分子(COMs)形成的原因。最近在T=4 K下进行的实验室实验表明,与富CO星际冰层类似的CO:N2冰样品在存在H2分子时,其辐照可能有助于COMs的形成。我们通过在4-15 K温度范围内用2 keV电子辐照CO:15N2:H2冰样品,测试了这种有机化学在更广泛的致密云内部相关条件下的表现。H2冰丰度既取决于冰的形成温度,也取决于样品的热演化。在辐照于高达10 K温度下形成的冰样品时,观察到了含氢有机物的形成,如甲醛(H2CO)、乙烯酮(C2H2O)和异氰酸(H15NCO);在6 K下形成并随后升温至高达15 K进行辐照的冰中也观察到了这些物质。这些结果表明,致密云内部的一部分H2分子可能被困在星际冰幔的富CO层中,而该层的能量处理可能为ISM最冷区域中COMs的形成提供额外贡献。

英文摘要:

Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs). Recent laboratory experiments performed at T=4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4-15 K temperature range. The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K. These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM.

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