Note, however, that the bulk of the atmosphere is made up of nitrogen and oxygen molecules which don't absorb IR at all. (giss.nasa.gov)
An electrical charge — from lightning or a man - made source such as an electrical generator — splits atmospheric nitrogen and oxygen molecules into separate atoms. (scientificamerican.com)
The concentration of water vapor in the atmosphere reflects the number of molecules of water compared with the total number of air molecules (mainly nitrogen and oxygen). (eso.org)