The Effect of Pressure on Binary Solution Phase Transition and Fermi Resonance ——Comparing Pressure Effect for Binary Solution and Pure Liquid

The Raman spectra of binary solution (CCl₄ and C₆H₆) and pure liquid were measured up to pressures of 11 GPa. The results show that pressure effect on binary solution is different from that on pure liquid: When mixing two liquids, owing to the changes in the density of the solution, intermolecular distance decreases and interaction energy increases, the frequency shift (blue shift) of spectral bands increases, and the frequency shift of binary liquid is faster than pure liquid frequency shift. Phase transitions (spectral bands splitting) change earlier and natural frequency difference Δ ₀ increases with increasing pressure, while the Fermi resonance bands ν₁+ν₆ and ν₈ of benzene and ν₁+ν₄ and ν₃ of CCl₄ disappear as the pressure decreases gradually, the spectral bands with different compressibility have different speed, whereas CCl₄ has smaller density, longer bond, smaller force constant and larger compressibility and is easy to compress, C₆H₆ has larger density, smaller bond, larger force constant, smaller compressibility and is hard to compress. The frequency shift of CCl₄ is faster than benzene. In this paper we provide good reference on Raman bands assignment and certification under high pressure, and also provide methods and ideas for study of the different environment of high pressure effect, intermolecular interaction and solvent effect.