Spectroscopy

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An example of spectroscopy: a prism analyses white light by dispersing it into its component colors. Light dispersion of a mercury-vapor lamp with a flint glass prism IPNrdeg0125.jpg
An example of spectroscopy: a prism analyses white light by dispersing it into its component colors.

Spectroscopy is the field of study that measures and interprets electromagnetic spectrum. [1] [2] In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum.

Contents

Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of astronomy, chemistry, materials science, and physics, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances.

Historically, spectroscopy originated as the study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism. Current applications of spectroscopy include biomedical spectroscopy in the areas of tissue analysis and medical imaging. 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). [3]

Introduction

Spectroscopy is a branch of science concerned with the spectra of electromagnetic radiation as a function of its wavelength or frequency measured by spectrographic equipment, and other techniques, in order to obtain information concerning the structure and properties of matter. [4] Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers. Most spectroscopic analysis in the laboratory starts with a sample to be analyzed, then a light source is chosen from any desired range of the light spectrum, then the light goes through the sample to a dispersion array (diffraction grating instrument) and captured by a photodiode. For astronomical purposes, the telescope must be equipped with the light dispersion device. There are various versions of this basic setup that may be employed.

Spectroscopy began with Isaac Newton splitting light with a prism; a key moment in the development of modern optics. [5] Therefore, it was originally the study of visible light that we call color that later under the studies of James Clerk Maxwell came to include the entire electromagnetic spectrum. [6] Although color is involved in spectroscopy, it is not equated with the color of elements or objects that involve the absorption and reflection of certain electromagnetic waves to give objects a sense of color to our eyes. Rather spectroscopy involves the splitting of light by a prism, diffraction grating, or similar instrument, to give off a particular discrete line pattern called a "spectrum" unique to each different type of element. Most elements are first put into a gaseous phase to allow the spectra to be examined although today other methods can be used on different phases. Each element that is diffracted by a prism-like instrument displays either an absorption spectrum or an emission spectrum depending upon whether the element is being cooled or heated. [7]

Until recently all spectroscopy involved the study of line spectra and most spectroscopy still does. [8] Vibrational spectroscopy is the branch of spectroscopy that studies the spectra. [9] However, the latest developments in spectroscopy can sometimes dispense with the dispersion technique. In biochemical spectroscopy, information can be gathered about biological tissue by absorption and light scattering techniques. Light scattering spectroscopy is a type of reflectance spectroscopy that determines tissue structures by examining elastic scattering. [10] In such a case, it is the tissue that acts as a diffraction or dispersion mechanism.

Spectroscopic studies were central to the development of quantum mechanics, because the first useful atomic models described the spectra of hydrogen, which include the Bohr model, the Schrödinger equation, and Matrix mechanics, all of which can produce the spectral lines of hydrogen, therefore providing the basis for discrete quantum jumps to match the discrete hydrogen spectrum. Also, Max Planck's explanation of blackbody radiation involved spectroscopy because he was comparing the wavelength of light using a photometer to the temperature of a Black Body. [11] Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms and molecules. Spectroscopy is also used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature, density of elements in a star, velocity, black holes and more). [12] An important use for spectroscopy is in biochemistry. Molecular samples may be analyzed for species identification and energy content. [13]

Theory

The underlying premise of spectroscopy is that light is made of different wavelengths and that each wavelength corresponds to a different frequency. The importance of spectroscopy is centered around the fact that every element in the periodic table has a unique light spectrum described by the frequencies of light it emits or absorbs consistently appearing in the same part of the electromagnetic spectrum when that light is diffracted. This opened up an entire field of study with anything that contains atoms. Spectroscopy is the key to understanding the atomic properties of all matter. As such spectroscopy opened up many new sub-fields of science yet undiscovered. The idea that each atomic element has its unique spectral signature enabled spectroscopy to be used in a broad number of fields each with a specific goal achieved by different spectroscopic procedures. The National Institute of Standards and Technology maintains a public Atomic Spectra Database that is continually updated with precise measurements. [14]

The broadening of the field of spectroscopy is due to the fact that any part of the electromagnetic spectrum may be used to analyze a sample from the infrared to the ultraviolet telling scientists different properties about the very same sample. For instance in chemical analysis, the most common types of spectroscopy include atomic spectroscopy, infrared spectroscopy, ultraviolet and visible spectroscopy, Raman spectroscopy and nuclear magnetic resonance. [15] In nuclear magnetic resonance (NMR), the theory behind it is that frequency is analogous to resonance and its corresponding resonant frequency. Resonances by the frequency were first characterized in mechanical systems such as pendulums, which have a frequency of motion noted famously by Galileo. [16]

Classification of methods

A huge diffraction grating at the heart of the ultra-precise ESPRESSO spectrograph. A Taste of ESPRESSO.jpg
A huge diffraction grating at the heart of the ultra-precise ESPRESSO spectrograph.

Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques. The various implementations and techniques can be classified in several ways.

Type of radiative energy

The types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy. The types of radiative energy studied include:

Nature of the interaction

The types of spectroscopy also can be distinguished by the nature of the interaction between the energy and the material. These interactions include: [2]

Type of material

Spectroscopic studies are designed so that the radiant energy interacts with specific types of matter.

Atoms

Atomic spectra comparison table, from "Spektroskopische Methoden der analytischen Chemie" (1922). Welsbach Figure IV spektroskopische-lytischen-chemie-21.pdf
Atomic spectra comparison table, from "Spektroskopische Methoden der analytischen Chemie" (1922).

Atomic spectroscopy was the first application of spectroscopy. 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.

Modern implementations of atomic spectroscopy for studying visible and ultraviolet transitions include flame emission spectroscopy, inductively coupled plasma atomic emission spectroscopy, glow discharge spectroscopy, microwave induced plasma spectroscopy, and spark or arc emission spectroscopy. Techniques for studying x-ray spectra include X-ray spectroscopy and X-ray fluorescence.

Molecules

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 millimetre-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. [2] [19] [20] [21] [22]

Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser.

Crystals and extended materials

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.

Nuclei

Nuclei also have distinct energy states that are widely separated and lead to gamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows for nuclear magnetic resonance spectroscopy.

Other types

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

Applications

UVES is a high-resolution spectrograph on the Very Large Telescope. UVES on UT2-KUEYEN.jpg
UVES is a high-resolution spectrograph on the Very Large Telescope.

There are several applications of spectroscopy in the fields of medicine, physics, chemistry, and astronomy. Taking advantage of the properties of absorbance and with astronomy emission, spectroscopy can be used to identify certain states of nature. The uses of spectroscopy in so many different fields and for so many different applications has caused specialty scientific subfields. Such examples include:

History

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." [38] 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." [38] 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." [38] [ better source needed ]

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 = hν where h is the Planck 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.

Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford–Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough. Named series of lines include the principal, sharp, diffuse and fundamental series.

See also

Notes

  1. ↑ Duckett, Simon; Gilbert, Bruce (2000). Foundations of Spectroscopy. Oxford Science Publications. ISBN   978-0198503354.
  2. 1 2 3 Crouch, Stanley R.; Skoog, Douglas A.; Holler, F. J. (2007). Principles of instrumental analysis. Australia: Thomson Brooks/Cole. ISBN   9780495012016.
  3. ↑ Bartusiak, Marcia (2017-06-27), "Einstein's Unfinished Symphony: The Story of a Gamble, Two Black Holes, and a New Age of Astronomy", Einstein’s Unfinished Symphony, Yale University Press, doi:10.12987/9780300228120, ISBN   9780300228120, OCLC   1039140043, S2CID   246149887 , retrieved 2023-05-22 Google Books
  4. ↑ The Oxford American College Dictionary. G.P. Putnam's Sons. 2002. ISBN   9780399144158. OCLC   48965005.
  5. ↑ "Isaac Newton and the problem of color", Steven A. Edwards, AAAS.
  6. ↑ "1861: James Clerk Maxwell's greatest year". King's College London. 18 April 2011. Archived from the original on 22 June 2013. Retrieved 28 March 2013.
  7. 1 2 PASCO, "What is Spectroscopy?"
  8. ↑ Sutton, M. A. "Sir John Herschel and the Development of Spectroscopy in Britain". The British Journal for the History of Science, vol. 7, no. 1, [Cambridge University Press, The British Society for the History of Science], 1974, pp. 42–60.
  9. ↑ Lazić, Dejan. "Introduction to Raman Microscopy/Spectroscopy". Application of Molecular Methods and Raman Microscopy/Spectroscopy in Agricultural Sciences and Food Technology, edited by Dejan Lazić et al., Ubiquity Press, 2019, pp. 143–50, http://www.jstor.org/stable/j.ctvmd85qp.12.
  10. 1 2 Perelman, L. T.; Backman, V.; Wallace, M.; Zonios, G.; Manoharan, R.; Nusrat, A.; Shields, S.; Seiler, M.; Lima, C.; Hamano, T.; Itzkan, I.; Van Dam, J.; Crawford, J. M.; Feld, M. S. (1998-01-19). "Observation of Periodic Fine Structure in Reflectance from Biological Tissue: A New Technique for Measuring Nuclear Size Distribution". Physical Review Letters. 80 (3): 627–630. Bibcode:1998PhRvL..80..627P. doi:10.1103/PhysRevLett.80.627.
  11. ↑ Kumar, Manjit. Quantum: Einstein, Bohr, and the great debate about the nature of reality / Manjit Kumar.—1st American ed., 2008. Chap.1.
  12. ↑ "Spectra and What They Can Tell Us". Imagine the Universe!. NASA Goddard Space Flight Center. August 2013.
  13. ↑ Nonell, Santi; Viappiani, Cristiano. "Basic Spectroscopy". Photobiological Sciences Online.
  14. ↑ "Atomic Spectra Database", NIST.
  15. ↑ Saul, Louise. (April 6, 2020). "The Different Types of Spectroscopy for Chemical Analysis". AZoOptics. Retrieved on November 10, 2021.
  16. ↑ Isaac Asimov, Understanding Physics, Vol. 1, p.108.
  17. ↑ "A Taste of ESPRESSO" . Retrieved 15 September 2015.
  18. ↑ Mariani, Z.; Strong, K.; Wolff, M.; Rowe, P.; Walden, V.; Fogal, P. F.; Duck, T.; Lesins, G.; Turner, D. S.; Cox, C.; Eloranta, E.; Drummond, J. R.; Roy, C.; Turner, D. D.; Hudak, D.; Lindenmaier, I. A. (2012). "Infrared measurements in the Arctic using two Atmospheric Emitted Radiance Interferometers". Atmospheric Measurement Techniques. 5 (2): 329–344. Bibcode:2012AMT.....5..329M. doi: 10.5194/amt-5-329-2012 .
  19. ↑ Kroto, H. W. (1975). Molecular Rotation Spectra. Wiley. ISBN   9780471508533. OCLC   793428.
  20. ↑ Philip R. Bunker and Per Jensen (1998),Molecular Symmetry and Spectroscopy, 2nd ed. NRC Research Press, Ottawa ISBN   9780660196282
  21. ↑ Papoušek, Dušan; Aliev, Mamed Ragimovich (1982). Molecular Vibrational-rotational Spectra: Theory and Applications of High Resolution Infrared, Microwave, and Raman Spectroscopy of Polyatomic Molecules. Amsterdam: Elsevier Scientific Publishing Company. ISBN   9780444997371. OCLC   7278301.
  22. ↑ Wilson, Edgar B.; Decius, John C.; Cross, Paul C. (1980-03-01). Molecular Vibrations: The Theory of Infrared and Raman Vibrational Spectra. Courier Corporation. ISBN   9780486639413. OCLC   1023249001.
  23. ↑ 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.
  24. ↑ W. Demtröder, Laser Spectroscopy, 3rd Ed. (Springer, 2003).
  25. ↑ 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.
  26. ↑ Backman, V.; Wallace, M. B.; Perelman, L. T.; Arendt, J. T.; Gurjar, R.; Müller, M. G.; Zhang, Q.; Zonios, G.; Kline, E.; McGillican, T.; Shapshay, S.; Valdez, T.; Badizadegan, K.; Crawford, J. M.; Fitzmaurice, M. (July 2000). "Detection of preinvasive cancer cells". Nature. 406 (6791): 35–36. doi:10.1038/35017638. ISSN   1476-4687. PMID   10894529. S2CID   4383575.
  27. ↑ Murray, Kermit K.; Boyd, Robert K.; Eberlin, Marcos N.; Langley, G. John; Li, Liang; Naito, Yasuhide (2013). "Definitions of terms relating to mass spectrometry (IUPAC Recommendations 2013)". Pure and Applied Chemistry . 85 (7): 1. doi: 10.1351/PAC-REC-06-04-06 . ISSN   0033-4545.
  28. ↑ 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.
  29. ↑ 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.
  30. ↑ 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.
  31. ↑ "Media advisory: Press Conference to Announce Major Result from Brazilian Astronomers". ESO Announcement. Retrieved 21 August 2013.
  32. ↑ Brian Bowers (2001). Sir Charles Wheatstone FRS: 1802–1875 (2nd ed.). IET. pp. 207–208. ISBN   978-0-85296-103-2.
  33. ↑ Brand, John C. D. (1995). Lines of Light: The Sources of Dispersive Spectroscopy, 1800 – 1930. Gordon and Breach Publishers. p. 57. ISBN   978-2884491624.
  34. ↑ Wang, Xiping; Wacker, James P. (2006). "Using NIR Spectroscopy to Predict Weathered Wood Exposure Times" (PDF). WTCE 2006 – 9th World Conference on Timber Engineering. Archived from the original (PDF) on 2021-03-01. Retrieved 2009-06-22.
  35. ↑ Sher, D. (1968). "The Relativistic Doppler Effect". Journal of the Royal Astronomical Society of Canada. 62: 105. Bibcode:1968JRASC..62..105S.
  36. ↑ "Germany and France Will Stop Chick Culling". 22 July 2021.
  37. ↑ Grau-Luque, Enric; Guc, Maxim; Becerril-Romero, Ignacio; Izquierdo-Roca, Víctor; Pérez-Rodríguez, Alejandro; Bolt, Pieter; Van den Bruele, Fieke; Ruhle, Ulfert (March 2022). "Thickness evaluation of AlO x barrier layers for encapsulation of flexible PV modules in industrial environments by normal reflectance and machine learning". Progress in Photovoltaics: Research and Applications. 30 (3): 229–239. doi:10.1002/pip.3478. ISSN   1062-7995.
  38. 1 2 3 Andrew Fraknoi; David Morrison (October 13, 2016). "OpenStax Astronomy".

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<span class="mw-page-title-main">Infrared spectroscopy</span> Measurement of infrared radiations interaction with matter

Infrared spectroscopy is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance on the vertical axis vs. frequency, wavenumber or wavelength on the horizontal axis. Typical units of wavenumber used in IR spectra are reciprocal centimeters, with the symbol cm−1. Units of IR wavelength are commonly given in micrometers, symbol μm, which are related to the wavenumber in a reciprocal way. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. Two-dimensional IR is also possible as discussed below.

Fourier-transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the radiation, electromagnetic or not. It can be applied to a variety of types of spectroscopy including optical spectroscopy, infrared spectroscopy, nuclear magnetic resonance (NMR) and magnetic resonance spectroscopic imaging (MRSI), mass spectrometry and electron spin resonance spectroscopy.

Atomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions, at the scale of one or a few atoms and energy scales around several electron volts. The three areas are closely interrelated. AMO theory includes classical, semi-classical and quantum treatments. Typically, the theory and applications of emission, absorption, scattering of electromagnetic radiation (light) from excited atoms and molecules, analysis of spectroscopy, generation of lasers and masers, and the optical properties of matter in general, fall into these categories.

<span class="mw-page-title-main">Raman spectroscopy</span> Spectroscopic technique

Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified.

<span class="mw-page-title-main">Spectral line</span> A distinctive narrow spectral feature of chemical species

A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected ones of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible.

<span class="mw-page-title-main">Emission spectrum</span> Frequencies of light emitted by atoms or chemical compounds

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state. The photon energy of the emitted photons is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.

<span class="mw-page-title-main">Absorption spectroscopy</span> Spectroscopic techniques that measure the absorption of radiation

Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption of electromagnetic 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 function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.

In physics, atomic spectroscopy is the study of the electromagnetic radiation absorbed and emitted by atoms. Since unique elements have unique emission spectra, atomic spectroscopy is applied for determination of elemental compositions. It can be divided by atomization source or by the type of spectroscopy used. In the latter case, the main division is between optical and mass spectrometry. Mass spectrometry generally gives significantly better analytical performance, but is also significantly more complex. This complexity translates into higher purchase costs, higher operational costs, more operator training, and a greater number of components that can potentially fail. Because optical spectroscopy is often less expensive and has performance adequate for many tasks, it is far more common. Atomic absorption spectrometers are one of the most commonly sold and used analytical devices.

<span class="mw-page-title-main">Fluorescence spectroscopy</span> Type of electromagnetic spectroscopy

Fluorescence spectroscopy is a type of electromagnetic spectroscopy that analyzes fluorescence from a sample. It involves using a beam of light, usually ultraviolet light, that excites the electrons in molecules of certain compounds and causes them to emit light; typically, but not necessarily, visible light. A complementary technique is absorption spectroscopy. In the special case of single molecule fluorescence spectroscopy, intensity fluctuations from the emitted light are measured from either single fluorophores, or pairs of fluorophores.

In physics and physical chemistry, time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Most often, processes are studied after the illumination of a material occurs, but in principle, the technique can be applied to any process that leads to a change in properties of a material. With the help of pulsed lasers, it is possible to study processes that occur on time scales as short as 10−16 seconds. All time-resolved spectra are suitable to be analyzed using the two-dimensional correlation method for a correlation map between the peaks.

<span class="mw-page-title-main">Raman scattering</span> Inelastic scattering of photons by matter

In chemistry and physics, Raman scattering or the Raman effect is the inelastic scattering of photons by matter, meaning that there is both an exchange of energy and a change in the light's direction. Typically this effect involves vibrational energy being gained by a molecule as incident photons from a visible laser are shifted to lower energy. This is called normal Stokes-Raman scattering.

<span class="mw-page-title-main">Molecular physics</span> Study of the physical and chemical properties of molecules

Molecular physics is the study of the physical properties of molecules and molecular dynamics. The field overlaps significantly with physical chemistry, chemical physics, and quantum chemistry. It is often considered as a sub-field of atomic, molecular, and optical physics. Research groups studying molecular physics are typically designated as one of these other fields. Molecular physics addresses phenomena due to both molecular structure and individual atomic processes within molecules. Like atomic physics, it relies on a combination of classical and quantum mechanics to describe interactions between electromagnetic radiation and matter. Experiments in the field often rely heavily on techniques borrowed from atomic physics, such as spectroscopy and scattering.

<span class="mw-page-title-main">Absorption band</span> Range on the electromagnetic spectrum

In quantum mechanics, an absorption band is a range of wavelengths, frequencies or energies in the electromagnetic spectrum that are characteristic of a particular transition from initial to final state in a substance.

Ultrafast laser spectroscopy is a category of spectroscopic techniques using ultrashort pulse lasers for the study of dynamics on extremely short time scales. Different methods are used to examine the dynamics of charge carriers, atoms, and molecules. Many different procedures have been developed spanning different time scales and photon energy ranges; some common methods are listed below.

<span class="mw-page-title-main">Resonance-enhanced multiphoton ionization</span> Spectroscopy technique

Resonance-enhanced multiphoton ionization (REMPI) is a technique applied to the spectroscopy of atoms and small molecules. In practice, a tunable laser can be used to access an excited intermediate state. The selection rules associated with a two-photon or other multiphoton photoabsorption are different from the selection rules for a single photon transition. The REMPI technique typically involves a resonant single or multiple photon absorption to an electronically excited intermediate state followed by another photon which ionizes the atom or molecule. The light intensity to achieve a typical multiphoton transition is generally significantly larger than the light intensity to achieve a single photon photoabsorption. Because of this, subsequent photoabsorption is often very likely. An ion and a free electron will result if the photons have imparted enough energy to exceed the ionization threshold energy of the system. In many cases, REMPI provides spectroscopic information that can be unavailable to single photon spectroscopic methods, for example rotational structure in molecules is easily seen with this technique.

Chemical imaging is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time information. Hyperspectral imaging measures contiguous spectral bands, as opposed to multispectral imaging which measures spaced spectral bands.

Photoelectrochemical processes are processes in photoelectrochemistry; they usually involve transforming light into other forms of energy. These processes apply to photochemistry, optically pumped lasers, sensitized solar cells, luminescence, and photochromism.

<span class="mw-page-title-main">History of spectroscopy</span>

Modern spectroscopy in the Western world started in the 17th century. New designs in optics, specifically prisms, enabled systematic observations of the solar spectrum. Isaac Newton first applied the word spectrum to describe the rainbow of colors that combine to form white light. During the early 1800s, Joseph von Fraunhofer conducted experiments 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. Fraunhofer observed and measured dark lines in the Sun's spectrum, which now bear his name although several of them were observed earlier by Wollaston.

<span class="mw-page-title-main">Spectral line shape</span> Feature observed in spectroscopy

Spectral line shape or spectral line profile describes the form of an electromagnetic spectrum in the vicinity of a spectral line – a region of stronger or weaker intensity in the spectrum. Ideal line shapes include Lorentzian, Gaussian and Voigt functions, whose parameters are the line position, maximum height and half-width. Actual line shapes are determined principally by Doppler, collision and proximity broadening. For each system the half-width of the shape function varies with temperature, pressure and phase. A knowledge of shape function is needed for spectroscopic curve fitting and deconvolution.

<span class="mw-page-title-main">Spectroelectrochemistry</span>

Spectroelectrochemistry (SEC) is a set of multi-response analytical techniques in which complementary chemical information is obtained in a single experiment. Spectroelectrochemistry provides a whole vision of the phenomena that take place in the electrode process. The first spectroelectrochemical experiment was carried out by Theodore Kuwana, PhD, in 1964.

References

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