Figure 1.

Upper panel: Beer's law (black line) compared with concentration dependence of the normalized integrated absorbance (from 1600–1800 cm⁻¹, red line), the normalized change of the index of refraction at 1500 cm⁻¹ (green line), the normalized change of the index of refraction at 1693 cm⁻¹ (blue line), and the absorbance at the oscillator position (1700 cm⁻¹, pink line). Center panel: Index of refraction function. Lower panel: Index of absorption function for different concentrations of 0.5, 5, 10, 25 and 50 mol L⁻¹ (S*²=4900 L/(mol cm²), ${\tilde{v}}_0=$ 1700 cm⁻¹ γ=20 cm⁻¹).