Authors: Berdahl, P.; Espinoza, L.H.; Littlejohn, D.; Lucas, D.; Perry, D.L.

Source: Applied Spectroscopy, Volume 54, Issue 2, Pages 52A-77A and 159-330 (February 2000) , pp. 262-267(6)

Publisher: Society for Applied Spectroscopy

Abstract:

Near-infrared transmission spectroscopy can be complicated by the light scattering from heterogeneous materials. For the examination of an evolving system exhibiting such light scattering, transmission spectra near wavenumber upsilon = 10⁴ cm^-1 were obtained during the hydrolysis of FeCl₃ solutions. At first, the resulting turbid suspension of cigar-shaped beta-FeOOH particles exhibits single-particle scattering, including a Rayleigh regime (attenuation upsilon⁴). At later times, the scattering increases strongly as the particles aggregate, and becomes proportional to upsilon^alpha, with alpha 2, consistent with scattering models that interpret the structure of aggregates in terms of a fractal dimension d_f roughly equal to 2. In all cases investigated, the attenuation due to scattering is spectrally smooth and increases monotonically with wavenumber. It can be written in the simple form upsilon^alpha with 1 < = alpha < = 4. While over limited spectral ranges alpha may be taken independent of upsilon , over wide ranges it decreases with increasing upsilon. This behavior is consistent with the theoretical limits of alpha = 4 at upsilon = 0, and alpha = 0 at upsilon = Infinity. Overall, the results suggest that a useful form for simulating scattering backgrounds in near-infrared spectroscopy is A upsilon^alpha, with A and alpha fitted constants.

Keywords: NEAR-INFRARED SPECTROSCOPY; LIGHT SCATTERING; FRACTAL AGGREGATES; BETA-FEOOH PARTICLES; HYDROLYSIS; AKAGANEITE

Document Type: Research article

DOI: http://dx.doi.org/10.1366/0003702001949195

Publication date: 2000-02-01

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