[Study on Enhancing Characteristic Vibration of the Molecular Vibration Spectrum for BDE-15 Based on Solvent Effect]

In this paper, the molecular vibrational spectra (IR spectra and Raman spectra) of 4, 4'-dibrominated diphenyl ethers (BDE-15) in atmosphere and 24 kinds of solvents were calculated, at the B3LYP/6-31+G(d) level by density functional theory and self-consistent reaction field separately. Taking the spectra in atmosphere as benchmark, the spectra information of selected characteristic vibrations which were sensitive to the polarity of solvent were used to establish the solvent effect index system for BDE-15, evaluate the specific solvent effect on vibrational frequency, IR vibrational intensity, Raman vibrational intensity and comprehensive solvent effect of each solvent and search the organic solvent which significantly affected the frequency shift/intensity. From the view of molecular vibrational frequency, the characteristic vibrations sensitive to polarity of solvent (frequency shift > 1 cm⁻¹) are all correlated with stretching and out-surface bending vibrations, the solvent effect on the vibrational frequency of BDE-15 of 24 kinds of solvents are all insignificant, with the index values between 1.01-1.03, compared with standard index value 1 of atmosphere spectra. From the view of molecular vibrational intensity, 24 kinds of solvents have all strengthen the vibrational intensities of most of vibrations, locating at the high frequency region of Raman spectra and the middle/low frequency region of IR spectra. The solvents which enhance the vibrational intensities significantly (index value greater than 6 and 5 for IR and Raman intensity separately) include alcohols, acetonitrile, dimethyl sulfoxide, nitrobenzene, dimethyl sulfoxide. The solvent effect index values on Raman vibrational intensity of BDE-15 increase along with the dielectric constant of solvents from linear to logarithmic growth trend, while the solvent effect index values on IR vibrational intensity only leaving the linear relationship. The comprehensive solvent effect index values have presented the similar change trend with Raman vibrational intensities. The spectra information of BDE-153, BDE-154, BDE-209 were used to authenticate the application on PBDEs of the analysis method above for BDE-15, obtaining the solvent effect index values on vibrational intensities on BDE-153, BDE-154, BDE-209 of alcohols, acetonitrile, dimethyl sulfoxide, nitrobenzene are all greater than 6 or 5, which indicate the enhancing vibrational intensities method can be used to identification research on PBDEs based on molecule vibrational spectra further.