In the far-IR range, pure rotations of molecules in their gaseous form are mainly observed. Their interpretation remains difficult and often requires numerical simulation.

Mid-IR spectroscopy is the most common and provides access to the identification of chemical functions in a molecule.

In the near-IR, the wide and low-intensity bands observed correspond to combinations and overtones of vibrational modes. The applications of these analyses, found in quality control, often require data processing by chemometrics.