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An electron revolving around the nucleus may capture an incident photon.
Once that occurs, the electron is raised to a higher energy level and
thus changes its orbit to a one with a larger radius. While being in the
excited state, the electron reemits the photon after some time and returns
to the ground state. Note that one can observe the phenomenon involving
the emission of the photon and its immediate recapture upon change of
orbit (virtual photon emission). |