尘埃红外光谱模拟中的粒子形状模型
Laboratory-based grain-shape models for simulating dust infrared spectra
摘要：
用于尘埃矿物学和物理颗粒性质的热尘埃发射光谱分析依赖于实验室测量或计算的比较光谱。通常，这两种光谱之间的协议是不令人满意的，因为对光谱的晶粒形态的强烈影响。我们调查的能力的统计光散射模型与分布的形状因子（DFF模型）重现实验测得的红外消光光谱的颗粒是小的波长相比。我们利用新的实验光谱测量分散在空气中的颗粒形态的附带信息。对于计算，我们使用的DFF的球形颗粒的聚集体，以及对应于高斯随机球的紧凑的颗粒形状。不规则的颗粒形状需要类似于高斯随机球的DFF，其中σ =0.3，而圆形颗粒形状最适合于分形维数为2.4-1.8的分形聚集体。此外，我们使用拟合算法来获得各种实验室样品的最佳拟合DFF。通过这种方式，我们可以独立地从它们的红外光谱中获得关于颗粒形状的信息。对于各向异性材料，不同的晶轴需要不同的DFF。这是由于一个理论问题，这是固有的所有模型，只是平均的贡献结晶方向。
英文摘要：
Analysis of thermal dust emission spectra for dust mineralogy and physical grain properties depends on laboratory-measured or calculated comparison spectra. Often, the agreement between these two kinds of spectra is not satisfactory because of the strong influence of the grain morphology on the spectra. We investigate the ability of the statistical light-scattering model with a distribution of form factors (DFF model) to reproduce experimentally measured infrared extinction spectra for particles that are small compared to the wavelength. We take advantage of new experimental spectra measured for free particles dispersed in air with accompanying information on the grain morphology. For the calculations, we used DFFs that were derived for aggregates of spherical grains, as well as for compact grain shapes corresponding to Gaussian random spheres. Irregular particle shapes require a DFF similar to that of a Gaussian random sphere with sigma=0.3, whereas roundish grain shapes are best fitted with that of a fractal aggregate of a fractal dimension 2.4-1.8. In addition we used a fitting algorithm to obtain the best-fit DFFs for the various laboratory samples. In this way we can independently derive information on the shape of the grains from their infrared spectra. For anisotropic materials, different DFFs are needed for the different crystallographic axes. This is due to a theoretical problem, which is inherent to all models that are simply averaging the contributions of the crystallographic directions.
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