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A material's
absorption spectrum shows the fraction of incident
electromagnetic radiationElectromagnetic radiation is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation...
absorbedIn physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy, for example, to heat. The absorption of light during wave propagation...
by the material over a range of
frequenciesFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
. Atoms, for example, have absorption lines at
wavelengthIn physics, the wavelength of a sinusoidal wave is the spatial period of the wave – the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s corresponding to the differences between the
energy levelA quantum mechanical system or particle that is bound, confined spatially, can only take on certain discrete values of energy, as opposed to classical particles, which can have any energy. These values are called energy levels. The term is most commonly used for the energy levels of electrons in...
s of its
atomic orbitalAn atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons, in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. These functions...
s. Each
chemical elementA chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.Common examples of elements...
has a distinct absorption spectrum. Absorption spectra can therefore be used to identify the elements present in a gas or liquid. This method is used in deducing the presence of elements in
starA star is a massive, luminous ball of plasma that is held together by gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth. Other stars are visible in the night sky, when they are not outshone by the Sun...
s and other gaseous objects which cannot be measured directly. The complete absorption spectrum of a material will depend not only on the atoms present but also how they are combined into molecules, how those molecules are packed together and the environment the material is in (e.g., temperature, pressure, electromagnetic fields and other materials present).
See also
- Fraunhofer lines
In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer . The lines were originally observed as dark features in the optical spectrum of the Sun....
- Spectroscopy
Spectroscopy was originally the study of the interaction between radiation and matter as a function of wavelength . In fact, historically, spectroscopy referred to the use of visible light dispersed according to its wavelength, e.g. by a prism. Later the concept was expanded greatly to comprise...
- Absorption spectroscopy
Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a...
- Densitometry
Densitometry is the quantitative measurement of optical density in light-sensitive materials, such as photographic paper or film, due to exposure to light...
- cf. Emission spectrum
The emission spectrum of an element or compound is the relative intensity of electromagnetic radiation of each frequency emitted by atoms or molecules of that element or compound when they are excited....
- X-ray absorption spectroscopy
- Absorption (electromagnetic radiation)
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy, for example, to heat. The absorption of light during wave propagation...
- HITRAN
HITRAN - HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere. The original version was compiled by the Air Force Cambridge Research Laboratories...
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