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 and velocity. One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency.
A plot of amplitude vs. This plot is one type of spectrum, with the peak often referred to as a spectral line , and most spectral lines have a similar appearance. 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.
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.
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: . Spectroscopic studies are designed so that the radiant energy interacts with specific types of matter. 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.
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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. 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. Studies in molecular spectroscopy led to the development of the first maser and contributed to the subsequent development of the laser.
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. For instance, blackbody radiation is due to the thermal motions of atoms and molecules within a material.
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Journal of Electroanalytical Chemistry and Interfacial Electrochemistry , , David Hodul, K. Douglas Carlson.
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Buschmann, H. Prehn, H. Photoacoustic spectroscopy PAS and its application in photosynthesis research. Photosynthesis Research , 5 1 , Betteridge, P. Analytical Aspects of Photoacoustic Spectroscopy. Raghuvir Singh, L. Ramlingeswara Rao.
Distortion of the coordination polyhedron in mononuclear copper II complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper II complexes. Polyhedron , 3 2 , Singh, Seema Agrawal, R. Studies on the reaction products of bis 2-furanthiocarboxyhydrazidato m II with pyridine and carboxaldehydes. Polyhedron , 3 11 , Jeanette G. Raghuvir Singh. Electron spin resonance and optical resonance studies on copper II complexes with vanadate, molybdate and tungstate anions. J Etxebarria, J Fernandez. Photoacoustic spectra of transparent solids doped with localised absorbing centres.
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Journal of Solid State Chemistry , 48 2 , Gary A. West, Joseph J. Barrett, Donald R. Siebert, K. Virupaksha Reddy. Photoacoustic spectroscopy.
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