Effect of External Electric Field on the Spectral Characteristics of Bromobenzene

Aromatic compounds are widely existing in nature. They are stable, highly toxic, carcinogenic and teratogenic chemicals. Among them, bromobenzene (C6H5Br) is one of the organic pollutants that damage the natural environment and pose a serious threat to human health. The study of the influence of external electric field on the spectrum of bromobenzene has been widely used in atmospheric chemistry, combustion chemistry, environmental monitoring and other fields. In the present paper, density functional theory(DFT) at BPV86/6-311G(d, p) level are employed for the study of IR spectrum of bromobenzene in the external electric field. Based on the density functional theory, the UV-Vis spectra of bromobenzene molecules are obtained by the same method and basis set. In the actual measurement, it is difficult to obtain physical characteristics such as the infrared spectrum and UV-Vis spectrum of bromobenzene molecules under an electric field of a specified size and direction. The research shows that by comparing with the experimental values, the infrared spectrum and UV-Vis spectrum of bromobenzene calculated based on density functional theory have high accuracy and good resolution, and include a wider range of wavelengths. Therefore, these results can be used as a supplement to the experimental values, which provides a new method for theoretically studying the influence of the external electric field. Without the external electric field, due to the C-H bond vibration, the infrared spectrum of bromobenzene molecule has the strongest absorption peak at a wave number of 718 cm(-1), and an absorption peak with an intensity second only to the strongest peak at 1 455 cm(-1). The C-Br bond has two strong absorption peaks near 727 and 1 185 cm(-1). As the external electric field increases from 0 to 0.03 a. u., both infrared absorption peaks of the C-Br bond are red-shifted and the vibration intensity increases, C-H bond vibrations have similar changes. The charge transfers the Br atom from the 6C atom along with the C-Br bond, which greatly enhances the electronegativity of the Br atom, and the negative charge density of the 6C atom decreases slightly. Therefore, the Coulomb force between the 6C atom and the Br atom increases, and the vibration intensity of the C-Br bond infrared spectrum increases. In addition, the wavelength corresponding to the strongest peak of the UV-Vis spectrum shifted from 191.6 to 187.4 nm, and the molar absorption coefficient increased from 23, 402.171 to 28,885.125. These results provide a theoretical reference for studying the spectral detection of bromobenzene under an external electric field, and also have implications for studying the spectral detection methods of other organic pollutants.