Why is resonance absorption possible for visible light in atoms and molecules?

Resonance absorption is possible for visible light in atoms and molecules because the kinetic recoil energy ($E_R$) associated with the emission and absorption of visible light photons is extremely small—so small, in fact, that it is negligible compared to the natural energy uncertainty of the electronic transitions involved.1

In the photon picture, resonance absorption would theoretically be hindered because an atom must recoil when it emits or absorbs a photon, carrying away or requiring additional kinetic energy. For visible light, however, this recoil energy is insignificant relative to the broadening of the energy levels, allowing the absorption process to occur despite the conservation of momentum.1

This stands in contrast to gamma-ray photons, where the recoil energy is more than 10,000 times greater and the energy transitions are much more sharply defined. Consequently, resonance absorption of gamma rays by free nuclei is generally not possible; it requires the Mössbauer effect, where the nuclei are embedded in a solid lattice to absorb the recoil momentum, effectively reducing the recoil energy to nearly zero.12