Polarized Raman spectroscopy has been used to measure the deuterium isotope effect, (delta)pK = pKD2O – pKH2O, for the second ionization constant of sulfuric acid in the temperature range of 25 °C to 200 °C at saturation pressure. Results for pK in light water agree with the literature within ± 0.034 pK units at alltemperatures under study, confirming the reliability of the method. The ionization constant of deuterated bisulfate, DSO4-, differs significantly from previous literature results at elevated temperatures. This results in an almost constant (delta)pK ≈ 0.425 ± 0.076 over the temperature range under study. Differences in (delta)pK values between the literature and current results can be attributed to the effect of dissolved silica from cell components. The new results are consistent with (delta)pK models that treat the temperature dependence of (delta)pK by considering differences in the zero-point energy of hydrogen bonds in the hydrated product and reactant species. The phosphate hydrolysis equilibrium was measured between the temperatures of 5 °C and 80 °C and the borate/boric acid equilibrium between the temperatures of 25 °C and 200 °C. The high alkalinity and temperatures experienced by these two systems had a significant impact on the glass dissolution and equilibrium. / Raman spectroscopy was used to measure the small differences in ionization constants for weak acids/bases as a function of temperature. / University of Guelph, Atomic Energy of Canada Limited (AECL), Bruce Power, University Network of Excellence in Nuclear Engineering (UNENE), National Sciences and Engineering Research Council of Canada (NSERC), Natural Resources Canada, Ontario Power Generation (OPG), Canada Foundation for Innovation