Figure 4

Determination of T_X with Brillouin spectroscopy for salt bearing FIs.

(a) Comparison of Raman spectra at 20 °C (all normalized to unit area). The blue curve shows the OH stretching band of pure water. The spectrum from FI4 (red) exhibits a decrease at low shift and increase at high shift, typical of dissolved salt. A standard procedure³⁷ yields an equivalent NaCl molality m_Raman = 1.25 ± 0.05 mol kg⁻¹. The spectrum from a bulk aqueous solution of 1.25 molal NaCl is also shown (black) for direct comparison. (b) Brillouin shift Δf_B as a function of temperature for reference NaCl solutions. The curves designated by the solution molality m (in mol kg⁻¹) were calculated from literature data (see Methods). They agree well with the corresponding experimental data (symbols). (c) Δf_B(T) for FI4, with (open symbols) or without (closed symbols) bubble. The thin black curve is the calculated for a NaCl solution with molality 1.20 mol kg⁻¹. The thick red curve is the result of the linear fitting procedure on ; it intersects at T_X. (d) Uncertainty δT_X (± 1 standard deviation) on T_X determined with Brillouin spectroscopy, as a function of T_X. The solid curves were calculated with equation (4) (see Methods) for pure water and NaCl solutions with designated molalities (in mol kg⁻¹). The marker shows the error on T_X from the linear fitting procedure for FI3, as given in Table 1.