Pressure-induced hydration number change of the Eu3+ ion in aqueous EuCl3 solutions

We have carried out Raman spectroscopic measurements on aqueous EuCl3 . 20H2O solution as a function of pressure at room temperature. Pressure dependence of the frequency shift of the totally symmetric stretching vibration of the aquo-europium earth ion (vw) is examined in conjunction with the hydration number change. We found that the population of Eu3+ ion holding eight water molecules in their inner most hydration spheres increases with applied pressure, which means that the lower aquo-complexes become dominant species at high pressures.