Either of these GHGs will gain energy if they
absorb IR from the ground (or from GHGs in the atmosphere), but then when they collide with other
molecules (almost always N2 or O2) they will give
away that extra energy until they are at the same average energy as the rest of the air.
When a photon hits a
molecule, if it has too much energy, enough is
absorbed to boost an electron to the next higher orbit and the rest is immediately radiated
away.