Andrew Wallace, of Nayland College, asks :-

Why does infrared radiation get absorbed by carbon dioxide gas?

John Campbell, a physicist at the University of Canterbury, responded

If we hit a tuning fork or pluck a guitar string or tap a thin-walled glass the object resonates at a frequency particular to it.

Let us consider one process whereby light is absorbed by a molecule without chemically altering the molecule.

Molecules with ionic bonds absorb infrared radiation. Carbon dioxide is a good example. It is a linear molecule whereby two oxygen atoms are bonded to a carbon atom between them and their electrons are shared so that the oxygen and carbon atoms are charged oppositely.

Electromagnetic radiation applies an oscillating electric force to an electrically charged object.

When microwave radiation is shone onto a carbon dioxide molecule the carbon atom and the oxygen atoms oscillate with respect to each other. If we increase the frequency of the radiation to about thirty million million times a second (in the infrared region of the electromagnetic spectrum) we strike a frequency at which the atoms resonate. At this frequency the molecule strongly absorbs energy from the infrared beam in order to keep the resonance going.

This natural frequency of resonance of the carbon dioxide molecule forms the basis of the carbon dioxide laser which is the most efficient gas laser for turning electrical energy into infrared radiation. In New Zealand such lasers are used in industry to cut sheet steel and in women's hospitals for internal surgery.