Facile generation and storage of polycyclic aromatic hydrocarbon ions in astrophysical ices
Facile generation and storage of polycyclic aromatic hydrocarbon ions in astrophysical ices
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DOI：
10.1086/379595
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发表时间：
2003-10-20
影响因子：
4.9
通讯作者：
Allamandola, LJ
中科院分区：
文献类型：
--
作者：
Gudipati, MS;Allamandola, LJ
本文描述了真空紫外线（VUV）辐照含多环芳烃（PAHs）的富水宇宙冰类似物的原位紫外-可见吸收和发射研究。紫外辐射12 K含多环芳烃萘（h - 2o /C10H8 = 200）和4-甲基芘（H2O/C17H12 > 500）的水冰容易将多环芳烃转化为阳离子形式（PAH(+)）。在这些条件下，多环芳烃的光电离是主要的反应。这些离子被捕获并储存在冰中，温度在10到50 K之间，这是整个星际云和太阳系中冰的共同温度域。不同于在稀有气体基质中分离的多环芳烃在VUV照射后的典型电离率为15%，在水冰中，多环芳烃的光电离和储存进行得非常高效，而且几乎是定量的，电离率大于70%。当温度从50 K增加到150 K时，多环芳烃离子带逐渐减少，因为多环芳烃离子最终反应形成涉及水宿主的更复杂的有机物质。这些富含离子的冰的化学、光谱学和物理性质对分子云、彗星和行星等冰冷物体很重要。介绍了几个天体物理应用。
In situ ultraviolet-visible absorption and emission studies of vacuum ultraviolet (VUV) irradiated water-rich, cosmic ice analogs containing polycyclic aromatic hydrocarbons (PAHs) are described. VUV irradiation of 12 K water ices containing the PAHs naphthalene (H-2 O/C10H8 = 200) and 4-methylpyrene (H2O/C17H12 > 500) readily converts the PAHs into their cation form (PAH(+)). Under these conditions, PAH photoionization is the predominant reaction. These ions are trapped and stored in the ices at temperatures between 10 and 50 K, a temperature domain common to ices throughout interstellar clouds and the solar system. Unlike the similar to 15% ionization typical after VUV irradiation of PAHs isolated in rare-gas matrices, in water ice, PAH photoionization and storage proceed efficiently and almost quantitatively with a greater than 70% ionization yield. As the temperature is increased from 50 to 150 K, the PAH ion bands slowly diminish as the PAH ions ultimately react to form more complex organic species involving the water host. The chemical, spectroscopic, and physical properties of these ion-rich ices can be important in icy objects such as molecular clouds, comets, and planets. Several astrophysical applications are presented.