In photon absorption, an electron can only absorb a photon if its energy matches the energy difference between two specific energy levels. If a photon has more energy than required for a transition, the electron cannot absorb it, as the absorption probability is sharply peaked around the transition frequency, described by the equation hν = E_u - E_l. The absorption cross-section for these transitions is characterized by Lorentzian profiles with a very narrow width, approximately 10-4 Å, indicating that only photons with energies closely matching the transition can be absorbed.
PREREQUISITESPhysicists, chemists, and students studying quantum mechanics or atomic physics, particularly those interested in photon interactions and energy level transitions.