Raman Spectroscopic Study of Five Typical Plasticizers Based on Dft and Hf Theoretical Calculation

Abstract

Phthalic acid esters (PAEs) are the most commonly used plasticizers, which are widely used in various fields of people's life and work. Long-term or high levels of exposure to PAEs have a huge potential risk to human health. Nowadays, PAEs hazard events occur frequently, the PAEs detection and strict control have become a top priority. Raman spectroscopy technology has the characteristics of no sample pretreatment, fast detection speed, and can respond to molecular fingerprint information, so it has gradually been applied to the detection of PAEs. Currently, only one theoretical method is used to calculate the Raman theoretical spectra of PAEs, and there is no comparison of studies on different theoretical methods and different basis sets. Because there are some spurious peaks in the Raman spectra obtained by the theoretical method, analyzing the Raman peaks of PAEs by only one theoretical calculation method will lead to errors. In this study, the Raman spectra of five typical PAEs were obtained experimentally, then the common and unique peaks in the Raman spectra of five typical PAEs were determined. After that, the theories of Hartree-Fock (HF) and density functional theory (DFT) with different hybrid methods and basis sets were used to calculate the theoretical Raman spectra of five PAEs, and comparison of calculated spectra between different theories, hybrid methods and basis sets was conducted to determine the suitable theory with hybrid method and basis set for PAEs. Finally, the optimal theoretical Raman spectra and experimental Raman spectra were combined and analyzed to assign the Raman vibrations to the Raman peaks. The results indicate that DFT is more suitable for theoretical study of PAEs than HF. For hybrid methods of B3LYP and B3PW91 in DFT, B3LYP is more applicable to the theoretical study of PAEs. In four basis sets, 6-311G(d, p) obtains the theoretical Raman spectra for the five PAEs which are in the best agreement with the experimental Raman spectra. This study finds the optimal combination of theoretical method and basis set for PAEs, which is beneficial to the research and analysis with experimental data. And it can help to establish the Raman database for PAEs in the future and further development of research work on rapid non-destructive testing of PAEs.

Keywords: PAEs, Raman, DFT, HF, theoretical study