基于拉曼光谱实验与密度泛函理论的宝石级红珊瑚拉曼谱峰归属研究

doi:10.3964/j.issn.1000-0593(2021)01-0127-04

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Abstract 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^2-₃ 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 CC 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 CC 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.

Key words：Red Coral; Canthaxanthin; Density functional theory; Raman spectrum; Assignments of peaks

Received: 2019-12-16 Accepted: 2020-04-19

ZTFLH:

P575.4

Corresponding Authors: Andy Hsitien Shen E-mail: ahshen@foxmail.com

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2021)01-0127-04 OR https://www.gpxygpfx.com/EN/Y2021/V41/I01/127