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FT-IR microspectroscopy of extraterrestrial dust grains: Comparison of measurement techniques

机译：地外尘埃的FT-IR显微光谱：测量技术的比较

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Identification of astronomical dust composition rests on comparison of Infrared (IR) spectra with standard laboratory spectra; frequently, however, a single mineralogical composition is assumed for spectral matching. Advances in laboratory instrumentation have enabled very precise IR spectra to be measured on single grains and zones within grains; with a more complete set of spectral data for planetary dust, better compositional matches will be achieved for astronomical dust. We have compared several FT-IR spectroscopy techniques (open path transmission spectroscopy and diffuse reflectance spectroscopy of powders; microspectroscopy of single grains and powders and ATR spectroscopy of thin sections) to determine their utility for the direct measurement of the mid-IR spectra of small amounts of extraterrestrial grains. We have focussed our investigation on the spectra of the olivine series of silicates, (Mg,Fe)_2SiO_4, a species frequently identified as one of the major constituents of interstellar dust. The positions of three characteristic SiO_4 stretching bands at ～10.4, 11.3 and 12 μm were measured for comparison of the techniques. All methods gave satisfactory results, although care must be taken to guard against artefacts from sample thickness and orientation effects. Single grains hand-picked from meteorites can be analysed, but results are inaccurate if the grain size is too large ( > 1-10 μm). Spectra for single grains also show variations that arise from sample orientation effects. Once the analytical artefacts are taken into account, we found that measurement of powder with a diamond compression cell is best suited for the analysis of small amounts of materials.
机译：天文学粉尘成分的鉴定取决于红外（IR）光谱与标准实验室光谱的比较。但是，通常假设单个矿物成分用于光谱匹配。实验室仪器的进步使得可以在单个晶粒和晶粒内区域上测量非常精确的红外光谱。有了更完整的行星尘光谱数据集，天文学尘将获得更好的成分匹配。我们比较了几种FT-IR光谱技术（粉末的开路透射光谱和漫反射光谱;单颗粒和粉末的显微光谱以及薄切片的ATR光谱），以确定它们在直接测量小颗粒的中红外光谱中的效用外星粮食的数量。我们将研究重点放在橄榄石系列硅酸盐（Mg，Fe）_2SiO_4的光谱上，该硅酸盐通常被认为是星际尘埃的主要成分之一。测量了三个特征SiO_4拉伸带在〜10.4、11.3和12μm处的位置，以进行技术比较。尽管必须注意防止样品厚度和方向效应造成的伪影，但所有方法均能获得令人满意的结果。可以分析从陨石中手工挑选的单个晶粒，但是如果晶粒尺寸太大（> 1-10μm），结果将不准确。单晶粒的光谱也显示出由于样品取向效应而引起的变化。一旦考虑了分析伪像，我们发现使用金刚石压缩池测量粉末最适合分析少量材料。

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