New spectroscopic method for aqueous solutions: Raman xi-function dispersion for NaClO4 in water

摘要

A new Raman method is exemplified by xiequivalent to-RT[partial derivative ln(I-omega/I-REF)/partial derivativeX(1)](T,P,n2),n(3) for ternary NaClO4/D2O/H2O, or by xiequivalent to-RT[partial derivative ln(I-omega/I-REF)/partial derivativeX(2)](T,P) for binary NaClO4/H2O solutions. (Fundamental differences exist between xi and the chemical potential mu.) I-omega is the Raman intensity at omega, I-REF is the reference intensity, e.g., at the isosbestic frequency, X-2 is the H2O and X-1 the small D2O mol fraction, and n(2) and n(3) are constant mols of H2O and NaClO4, respectively. Maxima (max) and minima (min) were observed in xi versus omega (cm(-1)); xi(max)-xi(min)=Deltaxi(max). Deltaxi(max)=8050+/-100 cal/mol H2O for the coupled, binary solution OH stretch, and Deltaxi(max)=4200+/-200 cal/mol H bond for the decoupled, ternary solution OD stretch. The perchlorate ion breaks the H bonds in water. 8050 cal/mol H2O corresponds to the maximum tetrahedral Deltaxi(max) value for two H bonds, i.e., Deltaxi(max)=4025 cal/mol H bond, in agreement with the HDO Deltaxi(max)=4200+/-200 cal/mol H bond. [Deltaxi(max) is not the H bond enthalpy (energy).] Minima occur in xi at the peak omega values corresponding to the HDO/H2O and H2O ices, and maxima in xi at 2637+/-5 cm(-1) (OD) and 3575+/-10 cm(-1) (OH) correspond to the peak OD and OH stretching omega values from dense supercritical water. Enthalpy dispersion curves were also determined for saturated, binary, and ternary NaClO4 solutions and for D2O in H2O. The xi-function method is shown to be applicable to infrared absorbance spectra. (C) 2005 American Institute of Physics.