红珊瑚是一种珍贵的有机宝石, 自古以来因其红润的颜色与细腻的质地深受人们的喜爱与追捧。 颜色漂亮的天然红珊瑚产量稀少, 故有些红珊瑚会经过染色处理来改善其外观。 拉曼光谱测试是鉴定红珊瑚有无经过染色处理的有力手段, 故红珊瑚拉曼谱峰的归属对于鉴定有着重要的理论指导意义。 由于红珊瑚拉曼峰的归属问题一直没有被深入研究, 基于此, 该研究测试了三颗颜色深浅不同的红珊瑚( Corallium rubrum)的拉曼光谱。 同时, 使用量子化学程序Gaussian 16运用密度泛函理论计算了红珊瑚中色素分子角黄素的理论拉曼光谱。 创新性对比红珊瑚的实验拉曼光谱与角黄素分子的理论拉曼光谱, 并进一步分析红珊瑚拉曼峰的归属。 结果发现, 红珊瑚的拉曼光谱中主要有1 514, 1 295, 1 177, 1 125, 1 086和1 016 cm^-1拉曼峰, 其中1 086 cm^-1处的拉曼峰是方解石的$CO_3^{2-}$引起的。 红珊瑚的红色越深, 1 514, 1 295, 1 177, 1 125和1 016 cm^-1拉曼峰的强度越强, 反之, 红珊瑚的红色越浅, 这些拉曼峰的强度越弱。 红珊瑚拉曼光谱中的1 514, 1 295, 1 177, 1 125和1 016 cm^-1峰强与红珊瑚的红色深浅呈现出正相关的关系, 故推测这套拉曼峰是由红珊瑚中的色素产生的。 角黄素理论拉曼光谱中主要存在的拉曼峰位于1 512, 1 269, 1 189, 1 159和999 cm^-1处, 与红珊瑚实验拉曼光谱中的1 514, 1 295, 1 177, 1 125和1 016 cm^-1峰的形状位置高度吻合。 振动分析结果表明, 角黄素的1 512, 1 269, 1 189, 1 159和999 cm^-1拉曼峰分别是由C=C伸缩振动, C—H摇摆振动, C—C伸缩振动, C—C伸缩振动与甲基摇摆振动引起的。 因此将红珊瑚拉曼光谱中的1 514, 1 295, 1 177, 1 125和1 016 cm^-1峰归属为C=C伸缩振动, C—H摇摆振动, C—C伸缩振动, C—C伸缩振动与甲基摇摆振动。 使用密度泛函理论的计算方法研究了红珊瑚拉曼谱峰的归属并对红珊瑚的拉曼谱峰进行了指认, 为使用拉曼光谱鉴定红珊瑚提供了理论基础。 同时为研究这类生物宝石材料拉曼谱峰的归属提供了一种新的方法。

Red coral is a kind of precious organic gemstone material, and it has been popular with people since ancient times because of its beautiful red color and delicate texture. Natural red corals with beautiful colors are rare in production, so some red corals are dyed to improve their appearance. Raman spectroscopy is a powerful method to identify whether red coral has been dyed or not, so the assignments on Raman peaks of red coral have important theoretical significance for identification. However, the assignments have not been studied profoundly. Based on this, the Raman spectra of three red corals ( Corallium rubrum) with different red color saturation were collected. At the same time, the theoretical Raman spectrum of pigment molecule canthaxanthin in red coral was calculated by Density Functional Theory (DFT) using quantum chemistry program Gaussian 16. We innovatively compared Raman spectrum of red coral and theoretical Raman spectrum of canthaxanthin to further analyze the assignments on Raman peaks of red coral. The results show that there are peaks at 1 514, 1 295, 1 177, 1 125, 1 086 and 1 016 cm^-1 in the Raman spectra of red corals and the Raman peak at 1 086 cm^-1 belongs to $CO_3^{2-}$ in calcite. The darker the red color of coral is, the stronger the Raman peaks at 1 514, 1 295, 1 177, 1 125 and 1 016 cm^-1 are. On the contrary, the lighter the red color of coral is, the weaker the Raman peaks are. The intensities of Raman peaks at 1 514, 1 295, 1 177, 1 125 and 1 016 cm^-1 are positively correlated with the saturation of red the color, so it is presumed that these Raman peaks are produced by pigments in red corals. The main Raman peaks in the theoretical Raman spectrum of canthaxanthin are located at 1 512, 1 269, 1 189, 1 159 and 999 cm^-1, which correspond well to the Raman peaks at 1 514, 1 295, 1 177, 1 125 and 1 016 cm^-1 of red coral. The results of vibration analysis show that the Raman peaks at 1 512, 1 269, 1 189, 1 159 and 999 cm^-1 of canthaxanthin belong to C=C stretching, C—H rocking, C—C stretching, C—C stretching and methyl rocking respectively. Therefore, the peaks at 1 514, 1 295, 1 177, 1 125 and 1 016 cm^-1 in Raman spectrum of red coral are assigned to C=C stretching, C—H rocking, C—C stretching, C—C stretching and methyl rocking. In this study, the calculation method of DFT is innovatively used to study the assignments on Raman peaks of red coral and interpret the Raman peaks of red coral, which provides a theoretical basis for using Raman spectroscopy to identify red coral. It also provides a new method to study assignments on Raman peaks of this kind of gem biomaterials.