|
|||||
|
|
FT-IR microspectroscopy of extraterrestrial dust grains: Comparison of measurement techniques |
|
| Authors: | A Morlok M Köhler Monica M Grady |
| Institution: | a Department Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK b Department of Earth Sciences, Rokkodai-cho1-1, Nada-Ku, Kobe-City 657-8501, Hyogo, Japan c Institut für Planetologie, Wilhelm-Klemm-Strasse 10,48149 Münster, Germany d Department Astronomy, University College London, Gower Street, London, UK e Planetary Space Sciences Research Institute, The Open University, Walton Hall, Milton Keynes, Bucks MK7 6AA, UK |
| Abstract: | 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)2SiO4, a species frequently identified as one of the major constituents of interstellar dust. The positions of three characteristic SiO4 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. |
| Keywords: | Infrared Dust Technique: Spectroscopic Methods: laboratory |
| 本文献已被 ScienceDirect 等数据库收录！ | |