Infrared Radiation

Infrared radiation causes the warmth that is felt near hot objects such as a fireplace. Note that the warmth above a fire is caused by hot gaseous molecules as well as infrared radiation, whereas that felt at the side of a fire is due to the infrared alone.

Infrared radiation when absorbed by matter causes the amplitudes of vibrational processes in the molecule to increase. The atoms in a molecule are constantly in motion, with bonds continually stretching, compressing, and bending. When we speak of a bond length or a bond angle, we mean the equilibrium bond length and angle. The stretching, compressing, and bending of bonds are known as vibrations, so the absorption of infrared radiation by a molecule is said to increase the vibrational energy of the molecule.

A calculated representation of molecular motion.

Infrared spectrometers are used by chemists to help elucidate structures of molecules. This is done by correlating the vibrational energies of unknown molecules with those of known molecules.

Some of the solar radiation that strikes the earth is converted to infrared radiation which then gets absorbed by carbon dioxide in the atmosphere and reradiated back to the earth, causing a warming effect. An increase in carbon dioxide and other gases due to human endeavors is implicated in the general warming trend of the earth known as the greenhouse effect.

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