Investigation on molecular structure of molten Li2BeF4 (FLiBe) salt by infrared absorption spectra and density functional theory (DFT)

FLiBe (2LiF-BeF 2 ) molecular structure was investigated by infrared (IR) absorption spectroscopy combined with density functional theory (DFT) calculations. An instrument was designed and implemented to obtain the in situ IR absorption spectra of molten FLiBe salt. IR absorption spectrum of molten FLiBe salt was obtained at 600 °C and the spectra assignment were aided with the density functional theory (DFT) calculations, which indicated that liquid FLiBe salt can form fluoberyllate of [BeF 4 ] 2 − . The IR spectrum of FLiBe powder acquired at room temperature furthers to imply that [BeF 4 ] 2 − was formed and combined with two Li + to make neutral molecule of Li 2 BeF 4 . Based on the geometry optimization, absorption peaks were also assigned and detailed vibration information was supplied.