Raman Study of Sulfuric Acid at Low Temperatures

A Raman spectroscopic study has been carried out for aqueous sulfuric acid of various concentrations at room temperature and in the glassy state. Temperature dependence of the Raman spectra was also investigated from 44 to −40 °C. Anomalous Tg (glass transition temperature) behavior of the aqueous sulfuric acid solution at ∼86 wt % H2SO4 is interpreted in terms of ionic species involved in Raman spectral changes. It is shown that ionization of sulfuric acid increases exponentially with decreasing temperature. Complete ionization was attained up to ∼50 wt % H2SO4 concentration in glassy aqueous H2SO4 solution.