Abstract. Since solids are only sometimes seen en masse in a pure bulk form, and for liquids other than water almost never, a capability to model reflectance spectra from analytes deposited on various substrates would be highly advantageous. If available, the real, n ( ν ) , and imaginary, k ( ν ) , components of the complex refractive index, n∼ = n + ik, can be used to simulate infrared spectra, accounting for reflection, refraction, and absorption phenomena as a function of wavelength. We focus on using the Pacific Northwest National Laboratory (PNNL) derived n / k vectors for solid and liquid analytes deposited as thin layers on different types of substrates including conductors, such as aluminum, and inorganic dielectrics, such as glass. The model is an adaptation of the Monte Carlo ray trace modeling program, TracePro, extended through the use of its macrolanguage. The model is tested using thin films of organic liquids including silicone oil and no. 2 diesel fuel, as well as organic solids such as caffeine and acetaminophen on aluminum and glass. The predicted spectra for the solid films were compared to experimental hemispherical reflectance data measured using a Fourier transform spectrometer with an integrating sphere. The thickness of the calculated layer is a parameter for predicting the (transflectance) spectra and is obtained using the areal density measured from gravimetric methods to generate the thin-layer samples. Comparison of the calculated spectra with experimental hemispherical reflectance data shows excellent agreement, indicating promise for the use of measured n / k data to synthesize reference spectral data. In particular, accounting for the inhomogeneity of the deposits greatly improved the match with experimental data. Finally, the theoretical modeling shows that for thicker layers (ca. 20 to 100 μm) of typical organics possessing moderately strong k values, the longwave infrared features are often saturated and better spectral contrast is obtained from the overtone/combination bands in the shortwave infrared.

中文翻译：

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为光谱分析模拟基质上的分析物薄层：使用固体/液体 n 和 k 值来模拟反射光谱

摘要。由于固体有时仅以纯块状形式整体出现，而对于除水以外的液体几乎从未出现过，因此对沉积在各种基材上的分析物的反射光谱进行建模的能力将是非常有利的。如果可用，复折射率 n∼ = n + ik 的实数 n ( ν ) 和虚数 k ( ν ) 可用于模拟红外光谱，考虑反射、折射和吸收现象作为波长的函数。我们专注于使用太平洋西北国家实验室 (PNNL) 导出的 n/k 向量，用于在不同类型的基材上沉积为薄层的固体和液体分析物，包括导体（如铝）和无机电介质（如玻璃）。该模型是蒙特卡罗光线追踪建模程序 TracePro 的改编版，通过使用其宏语言进行扩展。该模型使用包括硅油和无硅油在内的有机液体薄膜进行测试。2 柴油，以及铝和玻璃上的有机固体，如咖啡因和对乙酰氨基酚。将固体薄膜的预测光谱与使用带有积分球的傅立叶变换光谱仪测量的实验半球反射数据进行比较。计算层的厚度是用于预测（透反射）光谱的参数，是使用从重量法测量的面密度获得的，以生成薄层样品。计算光谱与实验半球反射率数据的比较显示出极好的一致性，表明使用测量的 n / k 数据合成参考光谱数据的前景。特别是，考虑到沉积物的不均匀性，大大提高了与实验数据的匹配度。最后，理论模型表明，对于具有中等强度 k 值的典型有机物的较厚层（约 20 至 100 μm），长波红外特征通常是饱和的，并且从短波红外中的泛音/组合带获得更好的光谱对比度.