Infrared spectra of pyroxenes (crystalline chain silicates) at room temperature
Infrared spectra of pyroxenes (crystalline chain silicates) at room temperature
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DOI：
10.1093/mnras/staa2227
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发表时间：
2020-07
影响因子：
4.8
通讯作者：
J. Bowey;A. Hofmeister;E. Keppel
中科院分区：
文献类型：
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作者：
J. Bowey;A. Hofmeister;E. Keppel
辉石晶体在陨石中很常见，但由于实验室研究中的化学成分有限，在天文环境中很少有成分被识别。我们提出了定量的室温光谱的17镁，铁，钙轴承的原和单斜辉石，和钙辉石，以辨别趋势指示的晶体结构和广泛的组合物。使用金刚石对顶砧单元产生数据：我们的带强度比KBr或聚乙烯分散体中测量的带强度高出六倍，其中包括在数据处理中未解决的路径长度（从粒度）和表面反射的变化。辉石有不同的光谱：顽火辉石（En 99）只有两个谱带，在10.22和15.34 μm，是所有辉石共有的。当Mg被Ca或Fe取代时，峰值波长通常增加。然而，当铁的成分从0增加到60%时，镁铁辉石中的两个谱带向较短的波长移动，一个高强度谱带从11.6 μm移动到11.2 μ m，当铁增加到100%时，它保持在11.2 μm;它类似于通常识别为橄榄石或镁橄榄石的天文特征。在詹姆斯·韦伯太空望远镜获得的中红外仪器光谱中，13 - 16 μm之间的独特辉石谱带显示出了识别它们的希望。如果用拟议中的宇宙学和天体物理学空间红外望远镜获得数据，40 - 80 μm之间的许多辉石谱带可以诊断硅酸盐矿物学。我们的数据表明，在室温实验室波段的顽火辉石和波长为28 μm的10 − K的冷天文尘埃特征之间进行比较，可以识别出（Mg，Fe）-辉石，它们的Fe含量比真实值低7- 15%，因为一些温度变化模仿了一些成分变化。因此，一些天文硅酸盐可能含有比以前认为的更多的铁，更少的镁。
Crystals of pyroxene are common in meteorites but few compositions have been recognized in astronomical environments due to the limited chemistries included in laboratory studies. We present quantitative room-temperature spectra of 17 Mg-, Fe-, and Ca-bearing ortho- and clinopyroxenes, and a Ca-pyroxenoid in order to discern trends indicative of crystal structure and a wide range of composition. Data are produced using a diamond anvil cell: our band strengths are up to six times higher than those measured in KBr or polyethylene dispersions, which include variations in path length (from grain size) and surface reflections that are not addressed in data processing. Pyroxenes have varied spectra: only two bands, at 10.22 and 15.34 μm in enstatite (En99), are common to all. Peak wavelengths generally increase as Mg is replaced by Ca or Fe. However, two bands in MgFe-pyroxenes shift to shorter wavelengths as the Fe component increases from 0 to 60 per cent. A high-intensity band shifts from 11.6 to 11.2 μm and remains at 11.2 μm as Fe increases to 100 per cent; it resembles an astronomical feature normally identified with olivine or forsterite. The distinctive pyroxene bands between 13 and 16 μm show promise for their identification in Mid-Infrared-Instrumentspectra obtained with the James Webb Space Telescope. The many pyroxene bands between 40 and 80 μm could be diagnositic of silicate mineralogy if data were obtained with the proposed Space Infrared Telescope for Cosmology and Astrophysics. Our data indicate that comparison between room-temperature laboratory bands for enstatite and cold ∼10 − K astronomical dust features at wavelengths ≳28 μm can result in the identification of (Mg,Fe)- pyroxenes that contain 7–15 per cent less Fe– than their true values because some temperature shifts mimic some compositional shifts. Therefore some astronomical silicates may contain more Fe, and less Mg, than previously thought.