Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation.[1][2][3][4][5][6] In simpler terms, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum; indeed, historically, spectroscopy originated as the study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism. Matter waves and acoustic waves can also be considered forms of radiative energy, and recently gravitational waves have been associated with a spectral signature in the context of the Laser Interferometer Gravitational-Wave Observatory (LIGO).

An example of spectroscopy: a prism analyses white light by dispersing it into its component colors.

Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of physics, chemistry, and astronomy, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances. Important applications arise from biomedical spectroscopy in the areas of tissue analysis and medical imaging.







In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy E of a photon is related to its frequency ν by E = where h is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.


Classification of methodsEdit

A huge diffraction grating at the heart of the ultra-precise ESPRESSO spectrograph.[7]


Type of radiative energyEdit


Nature of the interactionEdit

The types of spectroscopy also can be distinguished by the nature of the interaction between the energy and the material. These interactions include:[5]

  • Absorption spectroscopy: Absorption occurs when energy from the radiative source is absorbed by the material. Absorption is often determined by measuring the fraction of energy transmitted through the material, with absorption decreasing the transmitted portion.
  • Emission spectroscopy: Emission indicates that radiative energy is released by the material. A material's blackbody spectrum is a spontaneous emission spectrum determined by its temperature. This feature can be measured in the infrared by instruments such as the atmospheric emitted radiance interferometer.[8] Emission can also be induced by other sources of energy such as flames, sparks, electric arcs or electromagnetic radiation in the case of fluorescence.
  • Impedance spectroscopy: Impedance is the ability of a medium to impede or slow the transmittance of energy. For optical applications, this is characterized by the index of refraction.
  • Coherent or resonance spectroscopy are techniques where the radiative energy couples two quantum states of the material in a coherent interaction that is sustained by the radiating field. The coherence can be disrupted by other interactions, such as particle collisions and energy transfer, and so often require high intensity radiation to be sustained. Nuclear magnetic resonance (NMR) spectroscopy is a widely used resonance method, and ultrafast laser spectroscopy is also possible in the infrared and visible spectral regions.
  • Nuclear spectroscopy are methods that use the properties of specific nuclei to probe the local structure in matter, mainly condensed matter, molecules in liquids or frozen liquids and bio-molecules.

Type of materialEdit



Atomic spectroscopy was the first application of spectroscopy developed. Atomic absorption spectroscopy and atomic emission spectroscopy involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due to electronic transitions of outer shell electrons as they rise and fall from one electron orbit to another. Atoms also have distinct x-ray spectra that are attributable to the excitation of inner shell electrons to excited states.

Atoms of different elements have distinct spectra and therefore atomic spectroscopy allows for the identification and quantitation of a sample's elemental composition. After inventing the spectroscope, Robert Bunsen and Gustav Kirchhoff discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to as Fraunhofer lines after their discoverer. A comprehensive explanation of the hydrogen spectrum was an early success of quantum mechanics and explained the Lamb shift observed in the hydrogen spectrum, which further led to the development of quantum electrodynamics.



The combination of atoms into molecules leads to the creation of unique types of energetic states and therefore unique spectra of the transitions between these states. Molecular spectra can be obtained due to electron spin states (electron paramagnetic resonance), molecular rotations, molecular vibration, and electronic states. Rotations are collective motions of the atomic nuclei and typically lead to spectra in the microwave and millimeter-wave spectral regions. Rotational spectroscopy and microwave spectroscopy are synonymous. Vibrations are relative motions of the atomic nuclei and are studied by both infrared and Raman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well as fluorescence spectroscopy.


Crystals and extended materialsEdit

The combination of atoms or molecules into crystals or other extended forms leads to the creation of additional energetic states. These states are numerous and therefore have a high density of states. This high density often makes the spectra weaker and less distinct, i.e., broader. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material. Acoustic and mechanical responses are due to collective motions as well. Pure crystals, though, can have distinct spectral transitions, and the crystal arrangement also has an effect on the observed molecular spectra. The regular lattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies.



Other typesEdit

Other types of spectroscopy are distinguished by specific applications or implementations:


UVES is a high-resolution spectrograph on the Very Large Telescope.[16]

There are several applications to spectroscopy in the field of medicine, physics, chemistry, and astronomy. Taking advantage of the properties of absorbance, spectroscopy can be used to identify certain states of nature. Such examples include:


The history of spectroscopy began with Isaac Newton's optics experiments (1666–1672). According to Andrew Fraknoi and David Morrison, "In 1672, in the first paper that he submitted to the Royal Society, Isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbow."[19] Newton applied the word "spectrum" to describe the rainbow of colors that combine to form white light and that are revealed when the white light is passed through a prism.

Fraknoi and Morrison state that "In 1802, William Hyde Wollaston built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the spectrum."[19] During the early 1800s, Joseph von Fraunhofer made experimental advances with dispersive spectrometers that enabled spectroscopy to become a more precise and quantitative scientific technique. Since then, spectroscopy has played and continues to play a significant role in chemistry, physics, and astronomy. Per Fraknoi and Morrison, "Later, in 1815, German physicist Joseph Fraunhofer also examined the solar spectrum, and found about 600 such dark lines (missing colors), are now known as Fraunhofer lines, or Absorption lines."[19][better source needed]

See alsoEdit


  1. ^ H. W. Kroto, Molecular Rotation Spectra, Wiley, New York, 1975 (Reprinted by Dover 1992)
  2. ^ Philip R. Bunker and Per Jensen, Molecular Symmetry and Spectroscopy, NRC Research Press, Ottawa, 1998 [1] ISBN 9780660196282
  3. ^ D. Papoušek and M. R. Aliev, Molecular Vibrational-Rotational Spectra Elsevier, Amsterdam, 1982
  4. ^ E. B. Wilson, J. C. Decius, and P. C. Cross, Molecular Vibrations, McGraw-Hill, New York, 1955 (Reprinted by Dover 1980)
  5. ^ a b Crouch, Stanley; Skoog, Douglas A. (2007). Principles of instrumental analysis. Australia: Thomson Brooks/Cole. ISBN 978-0-495-01201-6.
  6. ^ Herrmann, R.; C. Onkelinx (1986). "Quantities and units in clinical chemistry: Nebulizer and flame properties in flame emission and absorption spectrometry (Recommendations 1986)". Pure and Applied Chemistry. 58 (12): 1737–1742. doi:10.1351/pac198658121737. S2CID 96002955.
  7. ^ "A Taste of ESPRESSO". Retrieved 15 September 2015.
  9. ^ Evans, C. L.; Xie, X. S. (2008). "Coherent Anti-Stokes Raman Scattering Microscopy: Chemical Imaging for Biology and Medicine". Annual Review of Analytical Chemistry. 1: 883–909. Bibcode:2008ARAC....1..883E. doi:10.1146/annurev.anchem.1.031207.112754. PMID 20636101.
  11. ^ Brian Orr; J. G. Haub; Y. He; R. T. White (2016). "Spectroscopic Applications of Pulsed Tunable Optical Parametric Oscillators". In F. J. Duarte (ed.). Tunable Laser Applications (3rd ed.). Boca Raton: CRC Press. pp. 17–142. ISBN 978-1-4822-6106-6.
  13. ^ N. A. Sinitsyn; Y. V. Pershin (2016). "The theory of spin noise spectroscopy: a review". Reports on Progress in Physics. 79 (10): 106501. arXiv:1603.06858. Bibcode:2016RPPh...79j6501S. doi:10.1088/0034-4885/79/10/106501. PMID 27615689. S2CID 4393400.
  14. ^ Solli, D. R.; Chou, J.; Jalali, B. (2008). "Amplified wavelength–time transformation for real-time spectroscopy". Nature Photonics. 2 (1): 48–51. Bibcode:2008NaPho...2...48S. doi:10.1038/nphoton.2007.253.
  15. ^ Chou, Jason; Solli, Daniel R.; Jalali, Bahram (2008). "Real-time spectroscopy with subgigahertz resolution using amplified dispersive Fourier transformation". Applied Physics Letters. 92 (11): 111102. arXiv:0803.1654. Bibcode:2008ApPhL..92k1102C. doi:10.1063/1.2896652. S2CID 53056467.
  17. ^ Wang, Xiping; Wacker, James P. (2006). "Using NIR Spectroscopy to Predict Weathered Wood Exposure Times" (PDF). WTCE 2006 – 9th World Conference on Timber Engineering.
  18. ^ Sher, D. (1968). "The Relativistic Doppler Effect". Journal of the Royal Astronomical Society of Canada. 62: 105. Bibcode:1968JRASC..62..105S.
  19. ^ a b c Andrew Fraknoi; David Morrison (October 13, 2016). "OpenStax Astronomy".


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