Figure 4: Temperature dependence (10–60°C) of difference spectra of NMA in CCl4 ((a) 0.12 mol dm−3; (b) 0.25 mol dm−3; (c) 0.80 mol dm−3; (d) 2.5 mol dm−3; (e) 8.0 mol dm−3). The spectrum of pure liquid sample of NMA at 30°C was taken as a reference. The subtraction was carried out after the concentration and density corrections of the pure NMA and CCl4 solution samples. The 1470-nm band due to the free NH of monomer increases with increasing temperature and the 1520-nm band due to the free, terminal NH moiety of hydrogen-bonded NMA aggregates decreases with increasing temperature. The free, terminal NH moiety of the hydrogen-bonded NMA aggregates seems to be oversubtracted below 30°C as shown in Figures 4(c), 4(d), and 4(e).