Development and physical reason of IR spectral features during condensation and solid phase reactions of Fe-Mg silicate systems: IR studies focused on non-stoichiometric silicates

Fe-Mg硅酸盐体系缩合和固相反应过程中红外光谱特征的发展和物理原因：红外研究重点关注非化学计量硅酸盐

• 批准号: 145757902
• 负责人: Dr. Ralf Dohmen
• 金额: --
• 依托单位: Ames Research Center
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2010
• 资助国家: 德国
• 起止时间: 2009-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/145757902?language=en
• 关键词: Development; physical; reason; IR; spectral

Silicates are one of the most important dust components in astronomical environments. In fact, the existence of silicate grains has been revealed by means of high resolution infrared (IR) spectroscopic observations as well as by secondary ion mass-spectroscopic examinations of meteorites. However, the formation and evolution processes of silicates have not been well understood yet. It is expected that under the non-equilibrium conditions encountered in space the production of non-stoichiometric dust grains is most likely. Such non-stoichiometric dust grains show distinct IR spectral features as compared with the stoichiometric cases because IR band profiles from minerals are very sensitive to chemical and physical properties. Thus, chemical and physical variations of these compounds directly influence the complex optical constants of the systems. For the interpretation of observed spectra both experimentally determined and theoretically calculated spectra are employed. For the theoretical simulations the optical constants are the most important input parameters. Deriving optical constants of nonstoichiometric silicates from mid-IR spectra therefore is a pre-requisite for improving the accuracy of the model calculations as well as enhancing the understanding of chemical and physical properties of observed mineral species. Presently, mainly spectra of stoichiometric compounds are used for interpretation of observed spectra because of a lack of experimental data for non-stoichiometric compounds. Thus, we will investigate the role and effect that a disparity of metals (Mg, Fe, Ca, Al, Na) in silicates has on spectra and monitor how the IR spectral features undergo a change by use of FTIR spectrometer. The proportions of the abundant components such as Mg and Fe in silicates are a key to understand the possible chemical condensation paths of those minerals. Highly accurate complex optical constants will be determined by making use of IR ellipsometry. For this, high quality silicate samples with well-defined metal proportion in silicate systems will be prepared by pulsed laser deposition (PLD) at Ruhr University Bochum. This technique is highly versatile in producing thin films of refractory materials with various compositions. We will investigate chemical, physical, and optical properties of both stoichiometric and nonstoichiometric structures of silicates in detail for a deeper understanding of dust composition and dust processing mechanisms in protoplanetary and young debris disks.

硅酸盐是天文环境中最重要的尘埃成分之一。事实上，硅酸盐颗粒的存在已经通过高分辨率红外（IR）光谱观测以及陨石的二次离子质谱检查揭示出来。然而，硅酸盐的形成和演化过程还没有得到很好的理解。预计在空间遇到的非平衡条件下，最有可能产生非化学计量的尘埃颗粒。这种非化学计量比的尘埃颗粒显示出独特的红外光谱特征相比，化学计量比的情况下，因为红外波段轮廓的矿物是非常敏感的化学和物理性质。因此，这些化合物的化学和物理变化直接影响系统的复光学常数。为了解释观察到的光谱，采用了实验确定的光谱和理论计算的光谱。对于理论模拟，光学常数是最重要的输入参数。因此，从中红外光谱导出非化学计量硅酸盐的光学常数是提高模型计算的准确性以及增强对所观察到的矿物种类的化学和物理性质的理解的先决条件。目前，由于缺乏非化学计量比化合物的实验数据，主要使用化学计量比化合物的光谱来解释观察到的光谱。因此，我们将研究硅酸盐中金属（Mg，Fe，Ca，Al，Na）的差异对光谱的作用和影响，并通过使用FTIR光谱仪监测IR光谱特征如何发生变化。硅酸盐矿物中镁、铁等丰富组分的比例是了解这些矿物可能的化学凝聚途径的关键。利用红外椭偏法可以测定高精度的复光学常数。为此，鲁尔大学波鸿将通过脉冲激光沉积（PLD）制备硅酸盐体系中具有明确金属比例的高质量硅酸盐样品。该技术在生产具有各种组成的耐火材料的薄膜方面是高度通用的。我们将详细研究硅酸盐的化学计量和非化学计量结构的化学，物理和光学性质，以便更深入地了解原行星和年轻碎片盘中的尘埃成分和尘埃处理机制。