Question

When a molecule absorbs a photon, what is the process called? When a molecule produces a photon, what is the process called?

Answer 1

Photoelectric effect is an example of electromagnetic wave (photon) getting absorbed by a particle. Photon transfers its energy to the particle and gets annihilated. The effect is based on the idea that electromagnetic radiation is made of a series of particles called photons.

Photon absorption by an atomic electron occurs in the photoelectric effect process, in which the photon loses its entire energy to an atomic electron which is in turn liberated from the atom. This process requires the incident photon to have an energy greater than the binding energy of an orbital electron. For X- and γ-ray photons of sufficient energy, photoelectric absorption is most likely to be caused by the most tightly bound electrons, i.e. those of the K shell, because the concentration of electrons is highest in this shell. Note that the photoelectric effect cannot occur if the electron is unbound, as it will not be possible to conserve both energy and momentum. The reaction is also favored at low photon energy and for atoms with a large atomic number, where there are many electron shells for the incoming photon to interact with, and to match in energy