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

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）光谱观测和陨石的二次离子质谱检查被揭示出来。然而，人们对硅酸盐的形成和演化过程还没有很好的了解。预计在太空中遇到的非平衡条件下，非化学计量尘埃颗粒的产生是最有可能的。这类非化学计量粉尘颗粒的红外光谱特征与化学计量粉尘颗粒不同，因为矿物的红外波段对化学和物理性质非常敏感。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。为了解释观测到的光谱，实验确定的光谱和理论计算的光谱都被采用。在理论模拟中，光学常数是最重要的输入参数。因此，从中红外光谱中得出非化学计量硅酸盐的光学常数是提高模型计算精度以及加强对所观察矿物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化合物的实验数据，主要采用化学计量化合物的光谱来解释观测到的光谱。因此，我们将研究金属（Mg, Fe, Ca, Al, Na）在硅酸盐中的差异对光谱的作用和影响，并利用FTIR光谱仪监测其红外光谱特征如何发生变化。硅酸盐中镁和铁等丰富成分的比例是了解这些矿物可能的化学凝聚路径的关键。利用红外椭偏法可以确定高精度的复光学常数。为此，在波鸿鲁尔大学，将采用脉冲激光沉积（PLD）技术制备高质量的硅酸盐样品，这些样品在硅酸盐体系中具有明确的金属比例。该技术在生产具有各种成分的耐火材料薄膜方面具有很高的通用性。我们将详细研究硅酸盐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组成和尘埃处理机制。

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.