拉曼光谱的16种多环芳烃（PAHs）特征振动光谱辨识

借助密度泛函理论中B3LYP/6-311++G(d, p)方法对美国EPA优先控制污染物中的16种多环芳烃(PAHs)：萘、苊烯、苊、芴、菲、蒽、荧蒽、芘、苯并[a]蒽、稠二萘、苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、二苯并(a, h)蒽、二苯并[g, h, i]芘以及茚苯(1, 2, 3-cd)芘进行结构优化，并计算拉曼光谱振动频率和去偏振度，在此基础上辨识多环芳烃的拉曼特征光谱。研究显示，16种PAHs的拉曼振动主要分布在3个频区：200～1 000 cm-1（指纹区）、1 000～1 700和3 000～3 200 cm-1（基团频率区），3个频区主要振动归属分别为环变形(ring def)，碳碳伸缩(CCStr)、碳氢摇摆(CHw)及其耦合振动(CCStrCCw)，碳氢伸缩(CHStr)。进一步分析显示，指纹区16种PAHs的去偏振度随苯环变形振动对称性增强而降低，在该频区去偏振度最小的频移处苯环呼吸振动的对称性最强，指纹区的峰强也在此处出现最大值。任意PAHs在指纹区的最强峰之间的波数差较大，在显微拉曼光谱的可分辨范围内，因而利用指纹区的去偏振度和最强峰可将16种PAHs逐一识别。烷烃、烯烃、炔烃、醇类和酚类、脂肪醚、芳基烷基醚、醛类、酮类、羧酸、酯类、胺类、腈类、酰胺类、酸酐、芳烃的振动频率和峰强分布不完全一致，利用PAHs与这几类物质拉曼频率和峰强分布的差异可以逐一排出干扰。

Identification of the Characteristic Vibrations for 16 PAHs Based on Raman Spectrum

In the present paper, by means of density functional theory in B3LYP/6-311++G(d, p) method, 16 kinds of pollutants, i.e. polycyclic aromatic hydrocarbons (PAHs): naphthalene (Nap), acenaphthylene (AcPy), acenaphthene (Acp), fluorene (Flu), phenanthrene (PA), anthracene (Ant), fluoranthene (Fl), pyrene (Pyr), benzo [a] anthracene (BaA), fused two naphthalene (CHR), benzo [b] fluoranthene (BbF), benzo [k] fluoranthene (BkF), benzo [a] pyrene (BaP), dibenzo (a, h) anthracene (DahA), dibenzo [g, h, i] pyrene (BghiP) and indene benzene (1, 2, 3-cd) pyrene (IcdP) among the U.S. EPA priority pollutants were selected, whose structures were optimized and Raman vibrational frequencies and depolarization were calculated. The structure, Raman vibrational frequencies and depolarization were basis of identification of PAHs. Studies have shown that Raman vibrations of 16 PAHs are mainly distributed in three frequency regions: 200～1 000 cm-1 (fingerprint region), 1 000～1 700 cm-1 and 3 000～3 200 cm-1 (group frequency region), corresponding vibrations were assigned to ring deformation (ring def), C—C stretching (CCStr), C—H wiggle (CHw) and of these two patterns (CCStrCCw), and C—H stretching (CHStr). Further analysis showed that in fingerprint region the depolarization of 16 PAHs was reduced with the symmetry of benzene deformation vibration enhanced. At the point of minimum depolarization, symmetry and Raman peak of benzene ring breathing vibration were found strongest. At the minimum differential wave number the strongest peak in fingerprint region was distinguishable by micro-Raman spectroscopy. Therefore, 16 PAHs can be individually identified by depolarization and the strongest peak in fringerprint region. Vibration frequencies and peak intensity distribution of alkanes (Akn), olefin (Oe), alkyne (Aye), alcohols and phenols (Aap), aliphatic ether (Ape), arylalkyl ether (Aae), aldehydes (Ahd), ketones (Ktn ), carboxylic acid (Cba), esters (Etr), amines (Aie), nitriles (Nte), amides (Aid), acid anhydride (Ahr), aromatic hydrocarbons (Ahc) were not completely consistent with each other, and interference can be discharged by the differences of frequency and peak intensity distribution.