Emission spectrum

An emission spectrum of the electromagnetic spectrum, which is emitted from atoms, molecules or materials, without the electromagnetic radiation of the same frequency is irradiated. The counterpart of an emission spectrum is the absorption spectrum. While discrete energy levels cause a line spectrum, call energy bands show a continuous spectrum.

Atomic spectrum

An atomic spectrum is the emission spectrum of a single isolated atom, ie the intensity of the light emitted by it ( emitted ) light as a function of the wavelength ( or frequency). The spectral lines correspond to the energy difference between two different states of the atom. This energy difference is, applied for example by an absorbed light particle, a photon, and then, with that energy emitted in the form of another photon, ie emitted. This energy (or in the spectrum of the line) is discrete, so it can not have any values ​​. This implies that each atom - can emit only discrete particles Wavelength - according to its electron configuration. The wavelengths of the emitted particles are therefore specific for a particular member. That the "lines" are exactly enough, curves having a predetermined width in the spectrum (, peak '), is based on quantum effects.

A comparison of the top two images ( 1, 2) shows that the spectral lines are wider with increasing gas pressure. At very high pressure, the line width can increase to such an extent that one observes a light continuum similar to a solid body. Cause is the frequent expectant mutual interference of atoms in collisions. The example of the spectral line at 491.6 nm can be seen that the relative intensity of this line is strongly dependent on the gas pressure.

In the picture below ( 3) one recognizes a different characteristic of the spectral lines for the element cadmium.

If by absorption of a photon, an electron completely detached from the atom is called ionization of the atom. This is dependent on the initial state of the electron, a certain minimum energy required. Since ionization is possible for a continuous energy range above the minimum energy, a continuum is possible. The reverse process, the emission of a photon in the capture of the electron is called a recombination of the electron with the positive ion. In this process, continuous radiation, the boundary continuum arises.

Molecular spectrum

A molecular spectrum is the result of a spectrum equal to the atomic spectrum described. However, the energy levels are mostly different and so are the relevant lines in the infrared.

Emission spectrum of a solid or liquid material

While the emission spectrum of dilute gases is a line spectrum, emit hot solids and liquids a continuous spectrum, because the individual atoms in addition interact with each other and thus the discrete quantum states merge. Such a continuous spectrum can be calculated by the spectrum of a black body ( Planck's radiation law ) multiplying the same temperature with the absorption coefficient of electromagnetic radiation of the " object " at the respective wavelength.