What Do We Know?

Now that we have a basic understanding of electromagnetic radiation, we can return to our original question: Do all gases interact with electromagnetic radiation in the same way?

Open the Collisional Heating Learning Tool. This tool shows the interactions of different gas molecules with infrared (IR) radiation. The first molecule you see is a carbon dioxide molecule. Move the scrubber bar at the top of the screen to one of the peaks in the spectrum and observe the interactions between the photons of electromagnetic radiation and the carbon dioxide molecule.

Next, select oxygen from the 'Gas' drop-down menu. Notice that there are no peaks in the spectrum at the top of the window. Observe the interaction between the oxygen molecule and photons of IR radiation.

You will have noticed that the carbon dioxide molecule absorbs the photons of IR radiation, causing the bonds of the molecule to bend and stretch. The oxygen molecule, however, does not interact with the photons in this infrared region of the electromagnetic spectrum. Our question is answered! Evidently, these two molecules do not interact with electromagnetic radiation in the same way.

In fact, the interactions between electromagnetic radiation and gases are highly dependent on the molecular structure of the gas in question, as well as the type of electromagnetic radiation that strikes the gas. Some gases absorb IR radiation while others do not interact with IR radiation at all. Also, even those molecules that do interact with IR radiation absorb at different wavelengths in the IR spectrum.

Your Turn

The interaction between IR radiation and gas molecules, which plays an important role in Earth's climate, is highly dependent on the type of gas that is involved. How do water molecules interact with photons of IR radiation? How do nitrogen molecules interact with IR photons? Use the Collisional Heating Learning Tool.

Why might different gases interact with electromagnetic radiation in different ways?