Here is more information about the main greenhouse molecules
To clarify and extend the description of units for the wavenumbers of infrared radiation, it is necessary to know that the wavelength of any electromagnetic radiation [infrared radiation, visible light and ultraviolet radiation are three familiar examples] is related to its frequency by the equation:
l = c/n
l is the symbol used for wavelength, c is the speed of light and n is the frequency of the radiation. The wavenumber is a useful unit because the numbers are manageable in the infrared region.
The vibrators [H2O, N2O and O3] are also capable of being encouraged to rotate by interacting [absorbing] infrared radiation. This is because they satisfy another of the quantum rules that specifies that such molecules should possess a permanent dipole moment. Those three molecules are the rotators.
CO2 is a linear molecule and cannot be induced to rotate by interaction with radiation; its vibrational motion can be caused by the absorption of infrared radiation only because the bending mode gives the molecule a transient dipole.
CH4 is a regular tetrahedral molecule and does not have a permanent dipole moment; it is not a rotator, but again it does have a vibrational mode which allows it to have a transient dipole moment.