Infrared analyses of clay mineral samples are usually performed by transmission techniques. While transmission measurements are easy and inexpensive, the sample preparation plays a critical role in the quality of the data. Alternatively, attenuated total reflection (ATR) provides a powerful and often simpler analysis method. However, the ATR spectra reveal significant differences when compared to transmission spectra sometimes leading to confusion in the interpretations. Indeed, optical effects play a prominent role in the ATR spectral profile and their identification is mandatory for obtaining quantitative information regarding molecular/particle orientation or film thickness. The objective of the present study was to perform exact spectral simulations of montmorillonite films by making use of optical theory, including the determination of the anisotropic optical constants from the experimental reflectance spectra by Kramers-Kronig (KK) transformation. This methodology was used: (1) to choose the appropriate optical conditions for advanced and reliable characterization of clay minerals; (2) to extract quantitative information such as the estimation of the film thickness; and (3) to discriminate optical phenomena (optical interferences) from chemical/structural features of the sample.

中文翻译：

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基于光学理论的蒙脱石薄膜衰减全反射红外光谱模拟

粘土矿物样品的红外分析通常通过透射技术进行。虽然传输测量既简单又便宜，但样品制备对数据质量起着至关重要的作用。或者，衰减全反射 (ATR) 提供了一种强大且通常更简单的分析方法。然而，与透射光谱相比，ATR 光谱显示出显着差异，有时会导致解释混乱。事实上，光学效应在 ATR 光谱剖面中发挥着重要作用，它们的识别对于获得有关分子/粒子取向或薄膜厚度的定量信息是必不可少的。本研究的目的是利用光学理论对蒙脱石薄膜进行精确的光谱模拟，包括通过 Kramers-Kronig (KK) 变换从实验反射光谱确定各向异性光学常数。该方法用于： (1) 选择合适的光学条件以进行粘土矿物的先进和可靠表征；(2)提取膜厚估计等定量信息；(3) 从样品的化学/结构特征中区分光学现象（光学干涉）。