LIBS和Raman光谱的VOCs在线探测

作为一种主要的大气污染物，挥发性有机物（VOCs）因其对大气环境极强的破坏性和生理毒性而受到广泛的关注，在线探测大气中挥发性有机物是一个极具挑战性的工作。将激光诱导击穿光谱（LIBS）与Raman光谱相结合，分别从原子发射光谱及分子结构信息角度对挥发性有机物进行了分析。在线原位检测得到的LIBS光谱观测到了Br元素特征谱线及N，O和H等空气所含元素特征谱线。实验成功探测到了挥发在空气中的邻氟溴苯，对于大气中溴的探测及其相关反应机理研究提供了支持。对于高能激光作用下产生的CN和C₂自由基分子，具体分析了二者产生机理。激光脉冲使空气中的氮气和邻氟溴苯的苯电离分解，邻氟溴苯中的碳原子与空气中的氮发生反应，会形成高温的等离子体，其中的碳氮原子再重新自由组合从而形成CN自由基并自发辐射，通过光谱仪可采集到该自由基的自发辐射的分子谱。待测样品邻氟溴苯分子含有苯环，分子中存在多个碳原子。在强激光作用下邻氟溴苯分子发生光解离，易于形成C₂自由基分子，并辐射产生C₂自由基光谱。实验验证了C₂自由基来自于邻氟溴苯样品里的苯环基团。为增加对挥发性有机物分子结构信息的了解，Raman光谱在线探测的引入很有必要。在样品Raman光谱实验结果的基础上，结合了密度泛函理论（DFT）对其振动模式及分布进行了计算拟合，对其振动产生的特征峰进行了标定并获得了其特征光谱指纹。强度较高的4个峰（310，833，1 036和1 244 cm-1）是C-Br键及C-F键振动表征，特别是前二者（310和833 cm-1）显示存在溴、氟原子位移，可作为该分子的特征光谱指纹对其进行识别。实验证明，LIBS与Raman光谱相结合应用至VOCs的在线探测具有很好的效果，对相关探测工作具有重要参考价值。

Online Detection of VOCs Based on LIBS and Raman Spectra

As the main substance of air pollution, volatile organic compounds (VOCs) have attracted wide attention because of their strong destructive and physiological toxicity to the atmospheric environment. On-line detection of volatile organic compounds in the atmosphere is a very challenging work. In this study, laser-induced breakdown spectroscopy (LIBS) was combined with Raman spectroscopy to analyze volatile organic compounds from the perspective of atomic emission spectroscopy and molecular structure information, respectively. The elements contained in the air, such as Br characteristic lines and N, O, H were observed in the LIBS spectra obtained by in-situ online detection. The experimental results reflect the detection effect of o-fluorobromobenzene in the air. For the detection of bromine in the atmosphere, LIBS reflects the presence of bromine in the atmosphere and provides a good reference for the study of its reaction mechanism. The mechanism of CN and C2 radical molecules produced by high energy laser was analyzed. The laser pulse can ionize and decompose nitrogen in the air and benzene of o-fluorobromobenzene. The carbon atom in o-fluorobromobenzene reacts with nitrogen in the air to form a high-temperature plasma. The carbon and nitrogen atoms in the plasma can be combined freely to form CN radical and spontaneous emission. The molecular spectrum of spontaneous emission of the free radical can be collected by the optical spectrometer. The o-fluorobromobenzene molecule of the sample to be tested contains a benzene ring, and there are many carbon atoms in the molecule. Under the action of the intense laser, o-fluorobromobenzene is photodissociated, which is easy to form C2 radical molecule, and the spectrum of C2 radical, as shown in the figure is produced by radiation. We can know that C2 radical comes from benzene ring group in o-fluorobromobenzene sample through experimental verification and data analysis. As a supplement to the molecular structure information of volatile organic compounds, the on-line detection of volatile organic compounds was improved by introducing Raman spectra. On the basis of the experimental results of the sample Raman spectrum, the vibration mode and distribution are calculated and fitted with density functional theory (DFT).The characteristic peaks generated by the vibration are calibrated, and the characteristic spectral fingerprints are obtained. The four peaks (310, 833, 1 036, 1 244 cm-1) with higher intensity showed C-Br bond and C-F bond vibration characterization, especially the former two (310, 833 cm-1) had bromine and fluorine atom shifts at the same time, which could be used as the characteristic spectral fingerprint to identify the molecule. The experimental results showed that the combination of LIBS and Raman spectrum was applied to the VOCs on-line detection, which has reference significance and value in its related detection work.