Density Functional Theory (DFT) and experimental measurements were used to develop a systematic method for interpreting the Raman spectra of hydrothermal char (hydrochar). Average band locations, relative intensities, and their trends relative to structural features were determined for the G, D, and Kekule bands. When combined with several other less prominent vibrational modes, including vibrations associated with aromatic, ether, alkyl, and carbonyl bonds, the calculated average locations reproduced all major features of hydrochar Raman spectra. Two model structures were found that could reproduce the main features of the hydrochar Raman spectrum and its elemental analysis: 1) a structure consisting of arene domains comprised of 6–8 rings connected via aliphatic chains or 2) a furan/arene structure consisting primarily of single furans and 2 or 3ring arenes. NMR confirmed that the furan/arene ratio of glucose hydrochar is approximately 1:1, consistent with the furan/arene structure supported by Raman spectra. This work establishes an interpretation method for hydrochar Raman spectra and reconciles the main features of hydrochar structures determined using Raman spectroscopy with those based on other methods.

中文翻译：

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基于振动光谱的密度泛函理论模拟热液炭及其模型的结构分析

密度泛函理论 (DFT) 和实验测量被用来开发一种系统的方法来解释热液炭 (hydrochar) 的拉曼光谱。确定了 G、D 和 Kekule 带的平均带位置、相对强度及其相对于结构特征的趋势。当与其他几种不太突出的振动模式结合时，包括与芳香键、醚键、烷基键和羰基键相关的振动，计算出的平均位置再现了水碳拉曼光谱的所有主要特征。发现两种模型结构可以再现水炭拉曼光谱及其元素分析的主要特征：1) 由通过脂肪链连接的 6-8 个环组成的芳烃结构域组成的结构，或 2) 主要由单呋喃和 2 或 3 环芳烃组成的呋喃/芳烃结构。核磁共振证实葡萄糖氢碳的呋喃/芳烃比约为 1:1，与拉曼光谱支持的呋喃/芳烃结构一致。该工作建立了水焦拉曼光谱的解释方法，并协调了使用拉曼光谱确定的水焦结构的主要特征与基于其他方法的结构特征。