Spectroscopy

Optical spectroscopy

Electrons exist in energy levels within an atom. These levels have well defined energies and electrons moving between them must absorb or emit an energy equal to the difference between them. (Energy is conserved.) In optical spectroscopy, the energy absorbed to move an electron to a more energetic level and/or the energy emitted as the electron moves to a less energetic energy level is in the form of a photon (a particle of light). Because this energy is well-defined, an atom's identity can be found by the energy of this transition. The wavelength of light can be related to its energy. It is usually easier to measure the wavelength of light than to directly measure its energy.

Optical spectroscopy can be further divided into absorption, emission, and fluorescence.

In atomic absorption spectroscopy, light is passed through a collection of atoms. If the wavelength of the light has energy corresponding to the energy difference between two energy levels in the atoms, a portion of the light will be absorbed. The relationship between the concentration of atoms, the distance the light travels through the collection of atoms, and the portion of the light absorbed is given by the Beer-Lambert law.