What are the properties of CO2 that cause it to radiate or reflect heat so well?
All polyatomic molecules with greater than 2 atoms interact with IR radiation, and all heteronuclear diatomic molecules interact with IR radiation. CO2 isn’t particularly special in that respect. But these requirements do count out a large portion of the atmosphere–> oxygen, argon and nitrogen gas do not interact with IR because they are nonpolar. That leaves gases like water vapor, CO2, methane and other trace gases to do the heavy lifting. Water vapor is by far the most abundant, and so contributes the most to the greenhouse effect. However, because CO2 is a linear molecule, it absorbs more frequencies of IR than H2O does, and thus is a better greenhouse gas. Methane has 5 atoms, and so absorbs at even more frequencies than CO2 does. In general, the more atoms that make up the molecule, the better greenhouse gas it is. To help explain why the above is true, think of the molecular bonds as springs connecting the atoms. For CO2, there is an oxygen atom on each side of the larger carbo