This is a description of the shapes and vibrations of the main greenhouse gas molecules

The shapes and important vibrations of the water molecule, H2O, carbon dioxide, CO2 and methane, CH4 are shown below.

The bending vibration of the water molecule is centered at a wavenumber of 1595 cm-1, that of CO2 occurs at 667 cm-1 and that of CH4 at 1306 cm-1. These vibrations are allowed by the quantum rule that states that, to interact with infrared radiation they must be accompanied by a change in dipole moment. A dipole moment is a charge separation in a molecule, e.g. in the hydrogen chloride molecule, HCl, the chlorine atom has a partial negative charge balanced by a partial positive charge on the hydrogen atom.

Other important greenhouse gases are nitrous oxide [dinitrogen monoxide] N2O and ozone [trioxygen] O3.

N2O is a linear molecule like CO2 and its symmetrical stretching vibration at 1285 cm-1 contributes to the greenhouse effect. The same vibration in triangular O3 where both bonds to the central oxygen atom extend and compress in-phase is very important in the stratosphere and absorbs at 1043 cm-1.

The units of wavenumbers are reciprocal centimetres [cm-1], and the values are the reciprocals of the wavelengths of the absorptions.