- One of the most common interactions used to explain the link between electromagnetism and light (including visible light and other parts of the spectrum) is the photon-electron interaction.
- The specific outcome of a photon-electron interaction depends on the photon’s energy and the electron’s state. For example, if the photon has enough energy, it can free a bound electron from the atom. This is known as the photoelectric effect.
- If the photon does not have enough energy to eject the electron, it can be scattered by the electron. Compton scattering involves high-energy photons, like X-rays or gamma rays, where the photon transfers part of its energy to the electron. The photon loses energy (shifts to a longer wavelength) and changes direction, while the electron gains kinetic energy.
- On absorption of a photon by an electron, the electron gains energy and transitions to a higher energy level – a higher orbital around the nucleus of the atom.
- When an electron scatters a photon elastically, such as in Rayleigh scattering, the photon alters its trajectory but retains its energy, and the electron’s energy level remains unaffected. In Compton scattering, however, the electron gains energy.
- A photon can transfer all of its energy to an electron if it has more energy than the electron’s binding energy. In this case, the electron will be ejected from the atom with excess kinetic energy.
- The amount of energy a photon can transfer to an electron is capped by the photon’s own energy. A photon cannot impart more energy to an electron than it possesses.
- The likelihood of a photon being absorbed by an electron depends on both the photon’s energy and the electron’s energy level. Absorption occurs when the photon’s energy exactly matches the difference between two energy levels (resonant absorption). Generally, higher photon energy increases the absorption likelihood, while higher electron energy levels tend to decrease the absorption probability due to fewer available transitions.
- The likelihood of photon scattering is influenced by the photon’s energy and the electron’s energy state. In Compton scattering, the angle of photon-electron collision affects the energy loss of the photon. Polarization of the photon and electron spin can also influence specific types of scattering, but spin is less central in general scattering processes.
- Examples of a photons-electron interaction include:
- Photoelectric Effect: When a photon with adequate energy impacts an electron, the electron can be expelled from the atom. Called the photoelectric effect, the photon’s energy must exceed the electron’s binding energy within the atom.
- Compton Scattering: In a collision between a photon and an electron, the photon can scatter. The photon might relinquish energy during the collision, and the electron can acquire a portion of the photon’s energy.
- Chromophore excitation: The photon-chromophore interaction accounts for the observable colour of objects.
- The interaction between photons and chromophores is more intricate than photon-electron interaction. It encompasses energy redistribution among all electrons in a molecule and can result in various outcomes such as fluorescence, phosphorescence, and energy transfer.
- The interaction between photons and chromophores is generally referred to as molecular excitation or chromophore excitation, distinct from photon-electron interaction but can still be considered a type of photon-electron interaction since it involves the interaction of photons with the electrons in chromophore molecules.
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