Is a pyrene-like molecular ion the cause of the 4,430-Å diffuse interstellar absorption band?
Is a pyrene-like molecular ion the cause of the 4,430-Å diffuse interstellar absorption band?
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类芘分子离子是 4,430-Å 漫射星际吸收带的原因吗？
DOI：
10.1038/358042a0
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发表时间：
1992
期刊：
影响因子：
64.8
通讯作者：
L. Allamandola
中科院分区：
文献类型：
--
作者：
Farid Salama;L. Allamandola
漫射星际带（DIBs）是天文光谱中普遍存在的吸收特征，自本世纪初以来就已为人所知，目前已有100多个。从4400 Å到近红外线2，它们在深度、宽度和形状上都有明显的不同，这使得单一载波的概念不太可能实现。究竟是气体还是颗粒造成的，目前还没有定论，但最近的研究结果表明，DIB载体与造成视觉消失的颗粒是完全分离的。在候选分子中，多环芳烃（PAHs）被认为是DIBs4-7的一些可能载体，我们在这里给出了在氖和氩矩阵中芘阳离子C16H10+的光谱的实验室测量结果。在氩基体和氖基体中，最强烈的吸收特征分别为4,435±5 Å和4,395±5 Å，均接近4,430-Å DIB。如果这个或一个相关的类芘物种负责这个特殊的波段，它必须占宇宙碳总量的0.2%。这种离子也表现出强烈但令人费解的宽连续体，从紫外线延伸到可见光，与萘阳离子类似，因此可能是所有多环芳烃阳离子的共同特征。这或许可以解释多环芳烃是如何将大部分星际辐射从紫外线和可见光波段转化为红外线的。
THE diffuse interstellar bands (DIBs), ubiquitous absorption features in astronomical spectra, have been known since early this century1 and now number more than a hundred. Ranging from 4,400 Å to the near infrared2, they differ markedly in depth, width and shape, making the concept of a single carrier unlikely. Whether they are due to gas or grains is not settled, but recent results3 suggest that the DIB carriers are quite separate from the grains that cause visual extinction. Among molecular candidates the polycyclic aromatic hydrocarbons (PAHs) have been proposed as the possible carriers of some of the DIBs4–7, and we present here laboratory measurements of the optical spectrum of the pyrene cation C16H10+ in neon and argon matrices. The strongest absorption feature falls at4,435 ± 5 Å in the argon matrix and 4,395 ± 5 Å in the neon matrix, both close to the strong 4,430-Å DIB. If this or a related pyrene-like species is responsible for this particular band, it must account for 0.2% of all cosmic carbon. The ion also shows an intense but puzzling broad continuum, extending from the ultraviolet to the visible, similar to what is seen in the naphthalene cation8 and perhaps therefore a common feature of all PAH cations. This may provide an explanation of how PAHs convert a large fraction of interstellar radiation from ultraviolet and visible wavelengths down to the infrared.