I have a hazy understanding from the atmospheric radiation course I took a decade back, but if I recall correctly the vibrational states of a two-atom molecule

I have a hazy understanding from the atmospheric radiation course I took a decade back, but if I recall correctly the vibrational states of a two-atom molecule are simply not at affected by infrared. To be a greenhouse gas, you need the, uh, rotational states provided by three or more atoms. Or something like that? I was always more of a dynamicist and barely scaped by in atm chem (it’s almost all free radical chemistry). Anyway you definitely need a third atom.