Figure shows the FTIR spectra of amorphous sorbitol from 113 -313 K acquired in 5 K increments. The frequency of the OH-stretch peak in the IR-absorption spectra exhibits the same temperature-dependent variation as measured using the other techniques, as shown in Figure , with clear changes in the slope being observed at both T gα and T gβ (Figure inset). The origins of the temperature-induced frequency shift must arise from a change in the OH-bond strength. Since the OH-bond potential energy surface is relatively hard (with the first excited vibrational level occurring at ≈ 5100 cm -1 , equivalent to ≈ 7300 K), only the vibrational ground state is populated under ambient conditions, indicating that the change in the OH-bond strength must arise from temperature-altered inter-molecular interaction strengths rather than higher order vibrational transitions (which would be expected to exhibit an anharmonically-caused red-shift in frequency with increasing temperature, rather than the observed blue-shift). Further evidence for this is the lack of any significant changes with temperature in the CH-bond stretch that occurs at ≈ 2900 cm -1 , since the CH-bond is not significantly influenced by inter-molecular interactions and there is little change in the CH-bond strength itself as a function of temperature.