Structure-dependent photostability of polycyclic aromatic hydrocarbon cations:: Laboratory studies and astrophysical implications
Structure-dependent photostability of polycyclic aromatic hydrocarbon cations:: Laboratory studies and astrophysical implications
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DOI：
10.1086/306752
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发表时间：
1999-02-10
影响因子：
4.9
通讯作者：
Leach, S
中科院分区：
文献类型：
--
作者：
Jochims, HW;Baumgärtel, H;Leach, S
继以前的一系列多环芳烃（PAHs）的光稳定性的实验研究，这项工作延伸到不规则形状的多环芳烃，甲基取代的多环芳烃，和相关的化合物。已经设计了一个光稳定性指数R，它测量的倾向H-损失的PAH单价相对于含有相同数目的原子的常规catacondensed或pericondensed多环芳烃。这个指数也是有效的，一个很好的近似，中性多环芳烃。结构的影响（存在的甲基;二氢基团; H-H位阻; π共轭度;异构体）和大小依赖的影响R的证明和讨论。天体物理应用的PAH光解离的倾向，包括估计的最大量的能量，可以沉积在新生的父PAH离子在H I区域，和评价的下限，在这些地区的光稳定的多环芳烃的大小，为各种类型的多环芳烃及其衍生物。结果提供了一个可能的解释，为存在的有限数量的多环芳烃在ISM所需的星际碳预算由雪和维特。获得的信息还与解释陨石、微陨石、彗星和行星际颗粒材料中多环芳烃及其甲基衍生物的存在和形成有关。
Following a previous experimental study of the photostability of a series of polycyclic aromatic hydrocarbons (PAHs) this work extends to irregularly shaped PAHs, methyl-substituted PAHs, and related compounds. A photostability index R has been devised, which measures the propensity for H-loss of PAH monocations relative to that for regular catacondensed or pericondensed PAHs containing the same number of atoms. This index is also valid, to a good approximation, for neutral PAHs. Structural effects (presence of a methyl group; dihydro groups; H-H steric hindrance; degree of pi conjugation; isomers) and size-dependent effects on R are demonstrated and discussed. Astrophysical applications of the propensity of PAH photodissociation include an estimation of the maximum amount of energy that can be deposited in the nascent parent PAH ion in H I regions, and an evaluation of the lower limit to the size of photostable PAHs in these regions, for various types of PAHs and their derivatives. The results provide a possible explanation for the existence of a limited number of PAHs in the ISM as required by the interstellar carbon budget determined by Snow & Witt. The information obtained is also relevant to interpretation of the presence and formation of PAHs and their methyl derivatives in meteoritic, micrometeoritic, cometary, and interplanetary particle materials.