No, simply a heat sink. It is an energy converter. It transforms IR radiation into mechanical (thermal energy). A heat sink is anything with sufficient specific heat, O2, N2, argon, would all work to some extent.
The attribute that makes some gases greenhouse gases is polarization. Because H2O and CO2 have different atoms, with different electronegativity, they are electrically polarized. They molecules are set spinning by an external electrical field, like the E-field associated with IR radiation. These molecules than collide with unpolarized molecules and some or the energy from their spinning is imparted to the unpolarized molecules, heating the whole atmosphere.
>> “ It transforms IR radiation into mechanical (thermal energy).” <<
.
You’re tripping over your own tongue here.
Have you ever owned a dictionary?
Mechanical energy is that which changes a state of motion.
All energy is thermal. Ever had a RF burn? It can burn holes through you just as efficiently as a laser, just not as predictibly in terms of position.