Raman spectra of samples under different pH conditions. Each spectrum represents the average of 1000 laser pulses. Measured spectra of standard NaHCO₃ and Na₂CO₃ powders are shown at the bottom of both panels for reference. (a) Spectra in the 400–1300 cm⁻¹ range. Raman peaks observed at approximately 673, 1045, and 1267 cm⁻¹ are assigned to vibrational modes of the bicarbonate ion (HCO﹩{}_{3}^{-}﹩). Raman peaks observed at approximately 686 and 1081 cm⁻¹ are assigned to vibrational modes of the carbonate ion (CO﹩{}_{3}^{2-}﹩). (b) Spectra in the 3200–4000 cm⁻¹ range.