Low Energy Bending Modes of Small Carbon Clusters: Laboratory Terahertz Spectroscopy

这里提出的研究的目的是在欧洲联合实验室-HiRes的框架内，将我们目前的研究扩展和扩展到一个新的领域，即迄今为止逃避实验室检测和光谱检查的假设星际分子。其中包括分子离子、直链分子和大的单环和多环。关键的创新将是一个非常敏感，但“便携式”太赫兹光谱仪的建设工作和探测我们的激光烧蚀技术产生的分子束。通过可调谐二极管激光光谱（IR-TDL）同时监测红外光谱和记录太赫兹光谱，我们预计这种新的，高度复杂的仪器在选择所需光谱方面比我们目前的光谱仪更加敏感，特别是当与质量选择光谱仪一起使用时。目前形式的太赫兹光谱仪已经是世界上最强大的，也是我们在这些频率上进行这种研究的唯一工具。大有机分子的实验室检测在几个方面都是有价值的。对这类物质的天文观测将增进我们对暗密分子云和富碳恒星的星周包层的物理和化学条件的了解。这些研究还将提供有关从线性到平面和环状结构的丰富过渡区域中的合成步骤的独特信息，这些数据是测试碳分子自组装理论所需的数据，包括富勒烯形成。最后，拟议的计划是针对一个主要的，长期存在的和未解决的问题，在天体物理学：载体（即原子或分子物种）的识别，引起弥漫星际带（DIb）。载体，现在通常被认为是相当大的分子，最有可能是含有长碳链的物质，是很重要的，因为它们可以构成自然界中所有化学键合物质的很大一部分。在过去的几个月里，我们已经制定了基本上所有的细节设计的新的TZZ光谱仪和它的成功连接到现有的TDL激光烧蚀分子喷射光谱仪，依赖于THz和IR光谱的同时测量。我们预计，这种下一代实验室光谱仪将很好地适应于更大的已知分子的弯曲运动或环起皱的测量。通过扩展，我们希望可以用它来检测假设的更大星际分子的实验室光谱。

The aim of the research proposed here within the framework of Associated European Laboratory-HiRes, is to extend and expand our present studies to a new domain of postulated interstellar molecules that have so far eluded laboratory detection and thus spectroscopic scrutiny. Amongst these are molecular ions, linear chain molecules and large monocyclic and polycyclic rings. The key innovation will be the construction of an extremely sensitive but "portable" THz spectrometer working with and probing the molecular beam produced by our laser ablation technique. By simultaneously monitoring the IR spectra by tunable diode laser spectroscopy (IR-TDL) and recording the THz spectrum, we expect that this new, highly sophisticated piece of instrumentation to be considerably more sensitive in selecting the wanted spectra than our current spectrometer, particularly when used together with a mass-selective spectrometer. The THz spectrometer in its present form is already the most powerful and only tool in the world for this kind of research we do at these frequencies. Laboratory detection of large organic molecules will be valuable in several ways. Astronomical observations of such species will improve our understanding of the physical and chemical conditions in dark and dense molecular clouds and circumstellar envelopes of carbon-rich stars. These studies also will provide unique information about the synthetic steps in the rich transition region from linear to planar and cyclic structures, data needed to test theories of carbon molecular self-assembly, including fullerene formation. And lastly, the proposed program is being directed towards a major, long standing and unsolved problem in astrophysics: the identification of the carriers (i.e. atomic or molecular species) which give rise to diffuse interstellar bands (DIbs). The carriers, now generally thought to be fairly large molecules, most likely long carbon chain containing species, are important because they may constitute by mass a significant fraction of all the chemically bonded matter in nature. Over the past few months we have worked out essentially all details of the design of the new TZz spectrometer and its successful attachment to the existing TDL laser ablation molecular jet spectrometer, relying on the simultaneous measurement of THz and IR spectra. We expect that this next generation laboratory spectrometer will be well adapted to the measurement of the bending motion or ring puckering of even larger known molecules. By extension we hope that the laboratory spectra of postulated even larger interstellar molecules can be detected with it.