Effect of D and 18O isotope substitution on the absorption spectra of aqueous copper sulfate solutions

The absorption spectra of 0.5 aquamolality solutions of copper sulfate (CuSO4) in H216O, D216O and H218O were determined at room temperature in the wavelength range of 400 - 1100 nm. Both deuterium (D) and 18O isotope substitutions resulted in a decrease of 6% and 1%, respectively, in the integrated absorption coefficient. No shift in the maximum of the absorption band was observed; the absorption band became narrower. The tint of the D216O solution is slightly greener than those of the H218O and H216O solutions. It is suggested that the observed isotope effects on the absorption spectra may mainly be ascribed to the change in the closest approach of the first coordination sphere water molecules to the Cu2+ ion brought about by isotope substitution.