Molecular structure and spectrum of dibutyl phthalate in an external electric field

Abstract

Dibutyl phthalate (DBP) is the main component of the plasticizers. In order to study the influence of an external electrical field on the molecular structure and spectra of DBP, the method B3LYP of the density functional theory (DFT) at 6-311++G(d, p) level has been used in this paper to calculate its geometrical parameters and infrared (IR) spectra, in the ground state of DBP molecule under different external electric fields (from 0 to 0.020 a.u.). On this basis, the UV-Vis absorption spectra of DBP are studied using the time-dependent density functional theory (TDDFT) in the same fundamental groups and compared with the ultraviolet(UV) absorption peak of the molecules measured by UNICO ultraviolet and visible spectrophotometer. The rule of variation of wavelength and oscillator strength of the first twenty-six excited states of a DBP molecule under the influence of the external electric fields are studied. Results show that the molecular geometric parameter is strongly dependent on the external field intensity, and the dipole moment of DBP is proved to be sharply increased, and the total energy first decreases with the increases of the external field intensity; the significant negative (“red”) and positive (“blue”) frequency shifts are observed, i.e., vibrational Stark effect (VSE) is shown obviously; the ultraviolet absorption peaks of the excited states of DBP show an observable red shift, and the oscillator strength decreases sharply with increasing field intensity.