Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published December 2009 | public
Journal Article

Mid-infrared reflectance spectra and optical constants of six iron oxide/oxyhydroxide phases

Abstract

We have determined the real and imaginary indices of refraction (n and k) for six iron oxide/oxyhydroxide phases—magnetite, maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite. A single crystal of magnetite was used to derive bulk n and k values from 100–2000 cm^(−1) (5–100 μm). Synthetic nanocrystalline samples of maghemite, goethite, lepidocrocite, akaganéite, and ferrihydrite were pressed into compact pellets used to determine bulk n and k values from 100–1200 cm^(−1) (8.33–100 μm). All values of n and k (the optical constants) were determined from specular reflectance spectra acquired at 2 cm^(−1) spectral sampling using classical Lorentz–Lorenz dispersion theory. In this paper, we present the optical constants of all six minerals and the oscillator parameters with which they were modeled. Use of these optical constants could aid in radiative transfer models of terrestrial dust as well as Mars, the Moon, and airless bodies in the Solar System.

Additional Information

© 2009 Elsevier Inc. Received 23 April 2009; revised 25 June 2009; accepted 3 July 2009. Available online 28 July 2009. We thank Brad DeGregorio for determining the average crystal shape and size of the synthetic maghemite powder. We also thank Richard Harrington for loaning us the ferrihydrite sample and Dick Morris for loaning us the goethite and lepidocrocite samples. Karly Pitman and an anonymous reviewer provided excellent reviews that enhanced the content and clarity of the manuscript. We acknowledge NASA Mars Fundamental Research Program Grant NNX06AB20G (to GRR) and the Stony Brook University College of Arts and Sciences for funding this work.

Additional details

Created:
August 22, 2023
Modified:
October 19, 2023