Aprism separates white light bydispersing it into its component colors, which can then be studied using spectroscopy.
Spectroscopy is the field of study that measures and interpretselectromagnetic spectra.[1][2] In narrower contexts, spectroscopy is the precise study ofcolor as generalized fromvisible light to all bands of the electromagnetic spectrum.
Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields ofastronomy,chemistry,materials science, andphysics, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic,molecular and macro scale, and overastronomical distances.
Spectroscopy is a branch of science concerned with thespectra ofelectromagnetic radiation as a function of its wavelength or frequency measured byspectrographic equipment, and other techniques, in order to obtain information concerning the structure and properties of matter.[4] Spectral measurement devices are referred to asspectrometers,spectrophotometers,spectrographs orspectral 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 aphotodiode. 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 withIsaac Newton splitting light with a prism; a key moment in the development of modernoptics.[5] Therefore, it was originally the study of visible light that we callcolor that later under the studies ofJames Clerk Maxwell came to include the entireelectromagnetic 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 ofquantum mechanics, because the first useful atomic models described the spectra of hydrogen, which include theBohr model, theSchrödinger equation, andMatrix mechanics, all of which can produce the spectral lines ofhydrogen, therefore providing the basis for discrete quantum jumps to match the discrete hydrogen spectrum. Also,Max Planck's explanation ofblackbody radiation involved spectroscopy because he was comparing the wavelength of light using a photometer to the temperature of aBlack Body.[11] Spectroscopy is used inphysical andanalytical chemistry becauseatoms andmolecules 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 inastronomy andremote sensing on Earth. Most researchtelescopes have spectrographs. The measured spectra are used to determine the chemical composition andphysical properties ofastronomical objects (such as theirtemperature, 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]
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 theperiodic 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. TheNational 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 andnuclear magnetic resonance.[15] In nuclear magnetic resonance (NMR), the theory behind it is that frequency is analogous toresonance and its corresponding resonant frequency. Resonances by the frequency were first characterized in mechanical systems such aspendulums, which have a frequency of motion noted famously byGalileo.[16]
A huge diffraction grating at the heart of the ultra-preciseESPRESSO spectrograph.[17]
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.
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:
The types of spectroscopy also can be distinguished by the nature of the interaction between the energy and the material. These interactions include:[2]
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'sblackbody 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.[18] Emission can also be induced by other sources of energy such asflames,sparks,electric arcs or electromagnetic radiation in the case offluorescence.
Elastic scattering andreflection spectroscopy determine how incident radiation is reflected or scattered by a material.Crystallography employs the scattering of high energy radiation, such as x-rays and electrons, to examine the arrangement of atoms in proteins and solid crystals.
Inelastic scattering phenomena involve an exchange of energy between the radiation and the matter that shifts the wavelength of the scattered radiation. These includeRaman andCompton scattering.
Coherent or resonance spectroscopy are techniques where the radiative energy couples two quantum states of the material in acoherent 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, andultrafast laser spectroscopy is also possible in the infrared and visible spectral regions.
Quantum logic spectroscopy is a general technique used inion traps that enables precision spectroscopy of ions with internal structures that precludelaser cooling, state manipulation, and detection.Quantum logic operations enable a controllable ion to exchange information with a co-trapped ion that has a complex or unknown electronic structure.
Atomic spectra comparison table, from "Spektroskopische Methoden der analytischen Chemie" (1922).
Atomic spectroscopy was the first application of spectroscopy.Atomic absorption spectroscopy andatomic emission spectroscopy involve visible and ultraviolet light. These absorptions and emissions, often referred to as atomic spectral lines, are due toelectronic 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 andGustav Kirchhoff discovered new elements by observing their emission spectra. Atomic absorption lines are observed in the solar spectrum and referred to asFraunhofer lines after their discoverer. A comprehensive explanation of thehydrogen spectrum was an early success of quantum mechanics and explained theLamb shift observed in the hydrogen spectrum, which further led to the development ofquantum 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 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 andRaman spectroscopy. Electronic excitations are studied using visible and ultraviolet spectroscopy as well asfluorescence spectroscopy.[2][19][20][21][22]
Studies in molecular spectroscopy led to the development of the firstmaser and contributed to the subsequent development of thelaser.
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 regularlattice structure of crystals also scatters x-rays, electrons or neutrons allowing for crystallographic studies.
Nuclei also have distinct energy states that are widely separated and lead togamma ray spectra. Distinct nuclear spin states can have their energy separated by a magnetic field, and this allows fornuclear magnetic resonance spectroscopy.
Electron phenomenological spectroscopy measures the physicochemical properties and characteristics of the electronic structure of multicomponent and complex molecular systems.
Hadron spectroscopy studies the energy/mass spectrum of hadrons according tospin,parity, and other particle properties. Baryon spectroscopy and meson spectroscopy are types of hadron spectroscopy.
Multispectral imaging andhyperspectral imaging is a method to create a complete picture of the environment or various objects, each pixel containing a full visible, visible near infrared, near infrared, or infrared spectrum.
Inelastic electron tunneling spectroscopy uses the changes in current due to inelastic electron-vibration interaction at specific energies that can also measure optically forbidden transitions.
Laser spectroscopy usestunable lasers[24] and other types of coherent emission sources, such as optical parametric oscillators,[25] for selective excitation of atomic or molecular species.
Mass spectroscopy is a historical term used to refer tomass spectrometry. The current recommendation is to use the latter term.[27] The term "mass spectroscopy" originated in the use ofphosphor screens to detect ions.
Multivariate optical computing is an all opticalcompressed sensing technique, generally used in harsh environments, that directly calculates chemical information from a spectrum as analogue output.
Raman optical activity spectroscopy exploits Raman scattering and optical activity effects to reveal detailed information on chiral centers in molecules.
Thermal infrared spectroscopy measures thermal radiation emitted from materials and surfaces and is used to determine the type of bonds present in a sample as well as their lattice environment. The techniques are widely used by organic chemists,mineralogists, andplanetary scientists.
Transient grating spectroscopy measures quasiparticle propagation. It can track changes in metallic materials as they are irradiated.
There are several applications of spectroscopy in the fields of medicine, physics, chemistry, and astronomy. Taking advantage of the properties ofabsorbance and withastronomy 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:
In-ovo sexing: spectroscopy allows to determine the sex of the egg while it is hatching. Developed by French and German companies, both countries decided to banchick culling, mostly done through a macerator, in 2022.[36]
The history of spectroscopy began withIsaac Newton's optics experiments (1666–1672). According toAndrew Fraknoi andDavid Morrison, "In 1672, in the first paper that he submitted to theRoyal 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 mechanicalstationary states of one system, such as anatom, via an oscillatory source of energy such as aphoton. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energyE of a photon is related to its frequencyν byE =hν whereh is thePlanck constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such aselectrons andneutrons have a comparable relationship, thede 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. Thehydrogen spectral series in particular was first successfully explained by theRutherford–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 thedensity of energy states is high enough. Named series of lines include theprincipal,sharp,diffuse andfundamental series.
Spectroscopy has emerged as a growing practice within themaker movement, enabling hobbyists and educators to construct functional spectrometers using readily available materials.[39] Utilizing components like CD/DVD diffraction gratings, smartphones, and 3D-printed parts, these instruments offer a hands-on approach to understanding light and matter interactions. Smartphone applications[40][41] along with open-source tools[42] facilitate integration, greatly simplify the capturing and analysis of spectral data. While limitations in resolution, calibration accuracy, and stray light management exist compared to professional equipment, DIY spectroscopy provides valuable educational experiences[43] and contributes to citizen science initiatives, fostering accessibility to spectroscopic techniques.
^Sutton, M. A. (1974). "Sir John Herschel and the Development of Spectroscopy in Britain".The British Journal for the History of Science.7 (1). Cambridge University Press:42–60.doi:10.1017/S0007087400012851.JSTOR4025175.
^Lazić, Dejan (2019). "Introduction to Raman Microscopy/Spectroscopy". In Radović, Biljana Vucelić; Lazić, Dejan; Nikšić, Miomir (eds.).Application of Molecular Methods and Raman Microscopy/Spectroscopy in Agricultural Sciences and Food Technology. London: Ubiquity Press. pp. 143–50.doi:10.5334/bbj.i.JSTORj.ctvmd85qp.12.
^Brian Orr; J. G. Haub; Y. He; R. T. White (2016). "Spectroscopic Applications of Pulsed Tunable Optical Parametric Oscillators". InF. J. Duarte (ed.).Tunable Laser Applications (3rd ed.). Boca Raton:CRC Press. pp. 17–142.ISBN978-1-4822-6106-6.
^Brand, John C. D. (1995).Lines of Light: The Sources of Dispersive Spectroscopy, 1800 – 1930. Gordon and Breach Publishers. p. 57.ISBN978-2-88449-162-4.
