Infrared Spectrum

There are many different forms of radiant energy -ultraviolet, visible, and infrafrared light, that differ in the wavelenght or frequency of the light. Infrared radiation has relatively long wavelengths (2 microns) and frequencies (2000 cm-1). It is the type of radiation that is given off by embers in a fire and which you sense as warmth. On a molecular microscopic scale infrared radiations is associated with molecular vibrations. We will be concerned primarily with the midle infrared region from 300cm-1 to 3000cm-1.

Molecular Vibrations

Atoms in a molecule do not maintain fixed positions but acutally vibrate back and forth about an average bond distances. Since this motion is microscopic it is quantized into descrete energy states by the laws of quantum mechanics. At room temperature most of the molecules will be in their lowest vibrational energy state or zero-point energy. Absorption of light with the approriate energy allows the molecule to become "excited" into the next higher vibrational energy state.