IR spectroscopy; a technique that measures absorption of electromagnetic radiation between the long wavelength end of the visible spectrum (780‒800 nm) and the short end of the microwave spectrum (1000 μm). In practice, most commercial IR spectrometers measure from 780 nm to 300 µm. Absorption in the IR is due to interatomic motions of molecules, vibrations and rotations about bonds. Spectra are commonly presented as percent transmission vs. wavelength.