Raman spectroscopy and quantum chemical calculation on YCl3-KCl molten salt system

The knowledge on the ionic structure of YCl 3 -KCl molten system is of guiding significance for the practical production of yttrium metals and yttrium alloys via molten salt electrolysis using this system as electrolyte. In this paper, the theoretical Raman spectra of the ionic groups which may exist in YCl 3 -KCl molten system are simulated by quantum chemical calculation using Gaussian 09 and GaussView 5.0 programs based on density functional theory (DFT). Then the ionic structures of 20 mol%–60 mol% YCl 3 -KCl molten salt systems are studied by comparing the Raman shift values of the bands in the theoretical Raman spectra of different ionic groups with the experimental spectra of this system. YCl 6 3− , Y 2 Cl 7 − , Y 2 Cl 8 2− and Y 2 Cl 9 3− are thought to exist in the molten system. With the increase of temperature, the relative content of YCl 6 3− ionic groups increases while those of Y 2 Cl 7 − , Y 2 Cl 8 2− and Y 2 Cl 9 3− ionic groups decrease. Moreover, the "lifetime" of all ionic groups decreases within the temperature range of 692–730 °C. Meanwhile, the relative contents of Y 2 Cl 7 − , Y 2 Cl 8 2− and Y 2 Cl 9 3− increase with the increase of YCl 3 content, while that of YCl 6 3− decreases. The wave function analysis of the four ionic groups (YCl 6 3− , Y 2 Cl 7 − , Y 2 Cl 8 2− , and Y 2 Cl 9 3− ) is carried out by Multiwfn program. The net charge in each group, the direction of electron migration during the formation of each group, the sites where electrophilic and nucleophilic reactions are most likely to occur in each ionic group, and the order of bond breaking during chemical reactions for the four groups are obtained. Graphical abstract