Abstract

It is well known that the antisymmetric stretching (ν₃) band in the mid-infrared spectra of oxyanion salts is usually very broad, whereas all the other fundamental bands are narrow. In this paper, we propose that the underlying cause of the increased width is the effect of the very high absorption index of this band for samples prepared with a range of particle sizes. When oxyanion salts are ground, the diameter of the resulting particles usually varies from less than 100 nm to about 2 µm. While the peak absorbance of the ν₃ band of the smaller particles (diameter < 200 nm) is less than 1, that of the larger particles can be as high as 6. We show that the average transmittance of these particles leads to a significant band broadening, especially when there are small voids in the resulting sample. Although the effect is always seen in the spectra of alkali halide disks and mineral oil mulls, it is also seen in diffuse reflection and attenuated total reflection (ATR) spectra. Because the depth of penetration of infrared radiation below 1500 cm⁻¹ is less than 1 µm for ATR spectra measured with a germanium internal reflection element (IRE), the width of the ν₃ band is lower than that of ATR spectra measured with an IRE of lower refractive index such as diamond on zinc selenide.

© 2018 The Author(s)

Widths of Infrared Absorption Bands in Liquids and Solids

John U. White and John N. Howard
J. Opt. Soc. Am. 46(8) 662-662 (1956)

A Comparison of the Widths of Liquid-Phase Infrared Absorption Bands and of the Corresponding Raman Bands

J. C. Evans
J. Opt. Soc. Am. 50(12) 1337-1338 (1960)

High band-width mid-infrared frequency-modulated Faraday rotation spectrometer for time resolved measurement of the OH radical

Feihu Cheng, Weixiong Zhao, Bo Fang, Yang Zhang, Nana Yang, Hao Zhou, and Weijun Zhang
Opt. Express 31(15) 25058-25069 (2023)

Infrared Spectra of Coal and Carbohydrate Chars

R. A. Friedel and M. G. Pelipetz
J. Opt. Soc. Am. 43(11) 1051-1052 (1953)

Fourier-transform infrared spectra of formaldoxime:ν₄, ν₅,ν₆, and ν₈ bands

R. A. Bannai and G. Duxbury
J. Opt. Soc. Am. B 11(1) 170-175 (1994)