Infrared laboratory absorbance spectra of olivine: using classical dispersion analysis to extract peak parameters

• Published in: Monthly notices of the Royal Astronomical Society 2010-07, Vol.406 (1), p.460-481
• Main Authors: Pitman, K. M., Dijkstra, C., Hofmeister, A. M., Speck, A. K.
• Format: Article
• Language: English
• Subjects: Astronomy; Dispersion; dust; dust, extinction; Earth, ocean, space; Exact sciences and technology; extinction; Infrared radiation; infrared: general; Measurement techniques; methods: laboratory; Parameter estimation; Spectrum analysis; techniques: spectroscopic
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2010.16669.x

Laboratory measurements quantifying the effect of Fe substituting for Mg in olivine are needed to distinguish compositional from temperature, grain size and grain shape effects in observational data. To address this need, we study room temperature absorption spectra of a large suite of olivines evenly spaced across Mg and Fe compositions. We apply the principle that classical dispersion theory may be used to determine peak positions as well as peak widths, strengths and possibly optical function (n(λ) and k(λ)) estimates from absorption spectra of thin film samples of these olivines and two additional isotropic and anisotropic minerals with varying hardness and numbers of spectral bands. For olivine, we find that this method provides good estimates of peak position and that accounting for asymmetric peak shapes in this way increases the error on full width at half-maximum and oscillator strengths. Values from classical dispersion fits better match published n and k derived from reflectivity of single crystals when the dust proxy is soft and the thickness of the sample is independently constrained. Electronic data and peak parameter trends for the laboratory olivine absorption spectra and the viability of the extracted n and k are discussed with regard to astronomy.