Why do molecules absorb Infrared radiation?

In basic terms, for a molecule to absorb radiation there has to be an oscillating dipole being produced. This can occur by nuclear motion (vibrations, rotations) or electronic motion to produce electronically excited states. read more

Infrared radiation is absorbed by a molecule when the frequency of the radiation matches that of one of the vibrational modes of the molecule. It is also necessary that the molecule have a vibrational mode for which there is a change in dipole moment. read more

Molecules absorb IR photons and gain energy which causes the bonds to vibrate. So carbon dioxide is a strong absorber in the IR (this is why it is a greenhouse gas). read more

Molecules of carbon dioxide (CO 2) can absorb energy from infrared (IR) radiation. This animation shows a molecule of CO 2 absorbing an incoming infrared photon (yellow arrows). The energy from the photon causes the CO 2 molecule to vibrate. read more