Near-Infrared Spectroscopy of Organic Substances

Abstract The near-infrared spectral region is generally defined as the wavelength range from 700 nm to about 2500 nm, although there is considerable variation in wavelength ranges of the different instrument types. The absorption bands in this region are due to overtones and combinations of the fundamental mid-IR molecular vibration bands. The energy transitions are between the ground state and the second or third excited vibrational states. Because higher energy transitions are successively less likely to occur, each overtone is successively weaker in intensity. Since the energy required to reach a second o r third level excited.