Contrary to the electronic transitions in molecules where the absorption occurs in the UV and visible light, vibration transition occurs at lower energy in the infrared region. To absorb infrared radiation, vibration transition (such as bond stretching behalf of atoms) to produce a change in dipole moment of molecules that can interact with the electric vector incoming radiation.Example:
HCl H <-> Cl
Because HCl is a polar molecule, changes in bond lengths will result in changes in dipole moment so that the HCl will absorb the infrared region. In other words, the non-polar molecules such as O2, N2 or Cl2 will not result in changes in dipole moment so that will not absorb in the infrared region. Carbon dioxide is also an interesting example because it has stretch yamg symmetry will not produce changes in the molecular dipole moment, so there will be no infrared absorption. On the other hand asymmetry stretching vibration will cause a change in dipole moment so that the infrared absorption occurs.
