Study on Vibrational Spectra of Cypermethrin Based on Density Functional Theory

As a broad-spectrum insecticide,Cypermethrin is widely used in various agricultural products,such as fruits, vegetables and poultry and so on.Because of its large dosage and slow degradation rate,drug residues in fruits,vegetables, livestock and other agricultural products are harmful to human health.In order to avoid human intake,it is very important to detect cypermethrin residues in agricultural products.Among the current detection methods,the vibration spectrum technology has the advantages of being non-destructive and fast.Therefore,this paper uses the density functional theory method combined with the vibration spectrum technology to provide a theoretical basis for the vibration spectrum detection and identification of Cypermethrin,and provide a reference for the application field of pesticide residue detection.The specific research contents and results are as follows:the first step is to construct the molecular space configuration of Cypermethrin by using Gaussian view software.Based on the DFT/B3LYP method of density functional theory,the structure is roughly optimized with a 3-21Gbasis set and then reoptimized with 6-311++G basis set based on coarse structure to obtain the stable configuration and frontier orbital distribution of the molecule.Then,based on the optimized structure,the theoretical infrared and Raman spectra of Cypermethrin were calculated.The theoretical results show that Cypermethrin has obvious infrared activity in the range of 3 300~3 000and 1 700~500cm~(-1).The former is mainly the vibration of functional groups,and the latter is the vibration of the fingerprint region.It can also be seen from the calculation results that the stretching vibration and scissor vibration of methylene hydrocarbon on cyclopropyl at 3 044and 1 459cm~(-1),the wagging vibration of methyne on cyclopropyl at 1 196cm~(-1)and the rocking vibration of hydrocarbon in benzene ring at 1 153cm~(-1)in Raman spectrum have no activity in the infrared spectrum.The cyano group without infrared activity shows a strong band in the Raman spectrum.The benzene ring skeleton vibration is weakly absorbed in the infrared spectrum but shows a strong band in the Raman spectrum.These reflect the complementary advantages of infrared spectroscopy and Raman spectroscopy.The combination of the two spectra is more conducive to the identification and detection of compound structure.In the second step,the natural Raman spectrum of Cypermethrin powder was measured by experimental method.The theoretical calculation error was corrected by the frequency correction factor of 0.973.The experimental results were compared with the theoretical calculation results.The difference in the peak frequency wavenumber was mostly in the range of 4~10cm~(-1),and the theoretical data were consistent with the experimental results.This study provides a theoretical basis for the vibration spectrum detection and structure identification of Cypermethrin,and provides a theoretical reference for its application in pesticide detection