A material's absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics, absorption of electromagnetic radiation is the process by which the Energy of a Photon is taken up by matter typically the electrons of an Frequency is a measure of the number of occurrences of a repeating event per unit Time. An absorption spectrum is, in a sense, the opposite of an emission spectrum. An element's 'emission spectrum' is the relative intensity of Electromagnetic radiation of each Frequency it emits when it is Heated (or more generally when Every chemical element has absorption lines at several particular wavelengths corresponding to the differences between the energy levels of its atomic orbitals. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. For example, an object that absorbs blue, green and yellow light will appear red when viewed under white light. Blue is a Colour, the Perception of which is evoked by Green is a Color, the perception of which is evoked by light having a spectrum dominated by energy with a Wavelength of roughly 520–570- nm. Yellow is the Color evoked by light that stimulates both the L and M (long and medium wavelength Cone cells of the Retina about equally Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength Absorption spectra can therefore be used to identify elements present in a gas or liquid. This method is used in deducing the presence of elements in stars and other gaseous objects which cannot be measured directly. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on Earth

Absorption spectrum observed by the Hubble Space Telescope

Explanation

Atoms and molecules may change states when they absorb specific amounts of energy. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by Atomic states are defined by the arrangement of electrons in atomic orbitals. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An atomic orbital is a Mathematical function that describes the wave-like behavior of an electron in an atom An electron in some orbital may be excited to a more energetic orbital by absorbing exactly one photon which has energy equal to the energy difference of the two orbitals. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena

Molecular states are defined by the molecule's modes of vibration and rotation. These vibrational and rotational modes are quantized, similar to the atomic orbitals, and may be excited by absorbing single photons.

In both the atomic and molecular cases, the excited states do not persist: after some random amount of time, the atoms and molecules revert back to their original, lower energy state. In atoms, the excited electron returns to a lower orbital, emitting a photon. In molecules, the vibrational or rotational mode decays, also emitting a photon.

When this decay occurs, the photon produced is not necessarily emitted in the same direction as the original photon. The most common angle of this has been shown to be about 45 degrees of the original photon. This applies to any situation where gases lie between a light source and an observer: the observer will see gaps in the spectrum of the light corresponding to the wavelengths of the photons which were absorbed. These gaps occur despite the re-emission of photons because the re-emitted photons are equally likely to travel in all directions, and it is statistically unlikely to travel along the original path to the observer. These gaps appear as black lines in an image of the spectrum. Black is the Color of objects that do not emit or Reflect Light in any part of the Visible spectrum; they absorb all such frequencies of

See also

• Fraunhofer lines
• Spectroscopy
• Absorption spectroscopy
• Densitometry
• cf. In Physics and Optics, the Fraunhofer lines are a set of Spectral lines named for the German physicist Joseph von Fraunhofer ( 1787 Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Absorption spectroscopy refers to a range of techniques employing the interaction of electromagnetic radiation with matter Densitometry is the quantitative Measurement of Optical density in light-sensitive materials such as Photographic paper or film, due to exposure Emission spectrum
• X-ray absorption spectroscopy
• Absorption (electromagnetic radiation)
• HITRAN

External links

• Solar absorption spectrum
• Visible Absorption Spectrum Simulation