Fig. 1. (a) Raman spectra and (b) excess Raman spectra in O-H stretching vibration interval of (NH4)2SO4 aqueous solution with different mass fractions

Fig. 2. Peak splitting data in O-H stretching vibration interval of (NH4)2SO4 aqueous solution with mass fractions of (a) 8.00% and (b) 12.00%

Fig. 3. Hydrogen bond structures in aqueous solution. (a) DDAA type; (b) DDA type; (c) DAA type; (d) DA type

Fig. 4. Hydrogen bond structures in (NH4)2SO4 aqueous solution with different mass fractions

Fig. 5. Integral area of positive peak of excess Raman spectra in O-H stretching vibration interval of (NH4)2SO4 aqueous solution versus mass fraction

Fig. 6. (a) Characteristic peak spectra and (b) normalized data of SO42- in (NH4)2SO4 aqueous solution with different mass fractions

Fig. 7. Excess Raman spectra of SO42- holosymmetric stretching vibration interval in (NH4)2SO4 aqueous solution with different mass fractions

Fig. 8. Variations of (a) positive peak integral area and (b) negative integral area of SO42- excess Raman spectra with mass fraction