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

Abstract

A new Raman method is exemplified by xi identical with-RT[ partial differential ln(I(omega)I(REF)) partial differentialX(1)](T,P,n(2),n(3) ) for ternary NaClO(4)D(2)OH(2)O, or by xi identical with-RT[ partial differential ln(I(omega)I(REF)) partial differentialX(2)](T,P) for binary NaClO(4)H(2)O 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 H(2)O and X(1) the small D(2)O mol fraction, and n(2) and n(3) are constant mols of H(2)O and NaClO(4), respectively. Maxima (max) and minima (min) were observed in xi versus omega (cm(-1)); xi(max)-xi(min)=Deltaxi(max). Deltaxi(max)=8050+/-100 calmol H(2)O for the coupled, binary solution OH stretch, and Deltaxi(max)=4200+/-200 calmol H bond for the decoupled, ternary solution OD stretch. The perchlorate ion breaks the H bonds in water. 8050 calmol H(2)O corresponds to the maximum tetrahedral Deltaxi(max) value for two H bonds, i.e., Deltaxi(max)=4025 calmol H bond, in agreement with the HDO Deltaxi(max)=4200+/-200 calmol H bond. [Deltaxi(max) is not the H bond enthalpy (energy).] Minima occur in xi at the peak omega values corresponding to the HDOH(2)O and H(2)O 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 NaClO(4) solutions and for D(2)O in H(2)O. The xi-function method is shown to be applicable to infrared absorbance spectra.