It is said that because of bond-structures / possible vibrational states, non-greenhouse-gases / homonuclear diatomics cannot absorb IR.
Presumably there is no question that all gases, being matter, can and do emit (mostly) IR photons at familiar temperatures - whether-or-not composed of IR-active—dipole-moment molecules.
Why the asymmetry (emit but not absorb)? What am I missing or misunderstanding?
(Forgive any imprecise use of terms by this sincerely-curious non-practitioner of the art.)