Figure 16: Temperature-induced evolution of the 𝜈 O H band contour shapes accompanying the variation in the contribution rate of the two different exciton coupling mechanisms, that is, “side-to-side” (SS) and “tail-to-head” (TH). Numerical reproduction of the temperature effect in the spectra of hydrogen-bonded (a) 2-furanacetic acid crystal (b) 2-furanacrylic acid crystal. The relative contribution ratio of the SS and TH mechanisms in the 𝜈 O H band generation is, for 2-furanacetic acid crystal: 0.95 : 0.05 at 293 K and 0.95 : 0.05 at 77 K and for 2-furanacrylic acid crystal: 0.65 : 0.35 at 293 K and 0.40 : 0.60 at 77 K. The experimental spectra are shown in inset.