Infrared spectra recorded of the same material at variable temperatures are shown to be useful in the making of vibrational assignments and in the elucidation of molecular structure. Functional groups such as OH, NH<sub>2</sub>, and C=O in compounds whose spectra have been recorded in CS<sub>2</sub> solution exhibit group frequencies which shift with change in temperature. Both variable-temperature and solution-phase studies are shown to be helpful in establishing that a compound exists as rotational isomers. Temperature changes are shown to vary the rotational isomer concentrations. The effect of temperature on difference tones, Fermi resonance, and in the breakdown of the selection rules is also demonstrated.
R. A. Nyquist, "The Significance of Temperature and Solvent Effects upon Infrared Spectra and Group Frequencies," Appl. Spectrosc. 40, 79-85 (1986)