Research On 16 PAHs Raman Spectrum Based On The Group Theory

The 16 polycyclic aromatic hydrocarbons(PAHs)nominated onAmerica Environmental Protection Agency(EPA) priority listare the most important environmental pollutans.The determination of PAHs is the key point of the monitoring and contamination control. Conventional annalysis methodsare rather conplicateed, while there are several advantages to using Raman spectroscopy foranalysis of water-rich and multi-component samples with celerity and facility. Sample preparation is not required for Ramanspectroscopy, which facilitates on-line quantitative analysis. However, the Raman peaks of PAHs molecules are rich and complex, and the Raman peaks with the same functional groups are highly overlapped which restrained Raman synchronous identification of 16 PAHs. This paper is dedicate to explorethe method of synchronous identification of 16 PAHsthe vibration law of the PAHs was analysised according to Group Thoery and the characteristic vibrations were identified based on the molecular symmetry, accordingly, the characteristic Raman peak of PAHs were recognized. Moreover, the effects of the surface environmental temperature and pressureon 16 PAHs were calculated to determine its stability of characteristic Raman peak that ascertained by Group theory. Specific researchof this paper includes the following aspects:(1) The character vibrations of PAHs were assigned based on Group Thoery. The symmetry elments of PAHs were identified according to the molecular geometry, in term of which assigned the point group of each PAHs melecular. The Raman shift distribution of functionnal group and vibration mode revealed thatthe vibration assignment of ring deformation, C-C stretching, C-H wiggle and coupled vibration of these two patterns and C-H stretching distributed in three regions; totally symmetric and full asymmetric vibration mode which contained vorious bond vibration pattern covered three regions, non-totally symmetri vibration mode located in fingerprint region.Further analysis showed that, all totally symmetric vibrations are raman-activehave and had higher Raman intensity activity, which can be used as PAHs characteristic Raman vibrations. Totally symmetric vibration instead of specific bond was identified as characteristic Raman vibrationavoid empiricaland the limitations of promotion.(2) Then, characteristic peaks 16 PAHs weredeterminedaccording to the symmetry mode combined with Gaussian 09 Calculation of Raman spectroscopy. The results showed that, totally symmetric vibration Raman peaks ofthe PAHs had same functional group and distribution region were raltive concentrated. This chacter can be used to deterined the existance of PAHs andeliminated interference other organic substance such as alkanes, alkenes, alkynes, alcohols and phenolic compounds. The Raman peaks of fingerprint region were sensitive to subtle differences in molecular structure,which were benifical of identification among 16 kinds of PAH. Non-totally symmetric vibration generated fingerprint region Raman peaks can be shielded by the polarization properties of the molecule, which were able to boost the resolution between 16 PAHs.(3) Finally, the surface ambient temperature pressure effects of PAHs Raman spectra were calculated by Gaussian09 density functional method to analyze the response of thermodynamics. The result revealed that, in the scope of thermal conditions changes, this Raman spectroscopy of PAHs in fingerprint region didn’t have significant displacement, characteristic Raman spectrum has certain stability in the range of surface ambient temperature and pressure virations.In conclution, the utilization of Group Theory which based on the symmetry of the molecular structureachieved the synchronization identification of PAHs byRaman spectra, and environment thermodynamic stability of PAHs Raman spectroscopy was ascertained.This paper is of great significance to environment online and in-situ monitoring of 16 PAHs.