Other Definitions
spectroscopy (dict)
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SpectroscopySpectroscopy is the study of spectra, ie. the dependence of a physical measure to frequency. Spectroscopy is often used in physical and analytical chemistry for the identification of substances, through the spectrum emitted or absorbed. A device for recording a spectrum is a spectrometer. Spectroscopy can be classified according to the physical quantity which is measured or calculated or the measurement process. Spectroscopy is also heavily used in astronomy. Physical quantity measured The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an amount or intensity of something. Measurement process Different types of spectroscopy use different measurement processes: Two main types of spectroscopy Absorption Spectroscopy uses the range of electromagnetic spectra in which a substance absorbs. It is more commonly used. In atomic absorption spectroscopy, the sample is atomized and then light of a particular frequency is passed through the vapour. After calibration, the amount of absorption can be related to the concentrations of various metal ions through the Beer-Lambert law. The method can be automated and is widely used to measure concentrations of ions such as sodium and calcium in blood. Other types of spectroscopy may not require sample atomization. For example, UV/Vis absorption spectroscopy is most often performed on liquid samples to detect molecular content and IR spectroscopy is most often performed on dried samples to to determine molecular information, including structureal information. Emission Spectroscopy uses the range of electromagnetic spectra in which a substance radiates. The substance first absorbs energy and then radiates this energy as light. This energy can be from a variety of sources, including collision (either due to high temperatures or otherwise), chemical reactions, and light. Common types of spectroscopy '''Fluorescence spectroscopy Fluorescence spectroscopy uses higher energy photons to excite a sample, which will then emit lower energy photons. This technique has become popular for its biochemical and medical applications, and can be used for confocal microscopy, fluorescence resonance energy transfer, and fluorescence lifetime imaging. X-ray spectroscopy and X-ray crystallography When X-rays of sufficient frequency (energy) interact with a substance, inner shell electrons in the atom are excited to outer empty orbitals, or they may be removed completely, ionizing the atom. The inner shell "hole" will then be filled by electrons from outer orbitals. The energy available in this de-excitation process is emitted as radiation (fluorescence) or will remove other less-bound electrons from the atom (Auger effect). The absorption or emission frequencies (energies) are characteristic of the specific atom. In addition, for a specific atom small frequency (energy) variations occur which are characteristic of the chemical bonding. With a suitable apparatus, these characteristic X-ray frequencies or Auger electron energies can be measured. X-ray absorption and emission spectroscopy is e.g. used in chemistry and material sciences to determine elemental composition and chemical bonding. X-ray crystallography is a process in which X-rays are shone onto crystals at a certain angle. The wavelength of the X-rays is known and so the distance apart of the crystal planes can be calculated. Combining all information enables crystal structure to be detected. Visible spectroscopy Many atoms emit or absorb visible light. In order to obtain a fine line spectrum, the atoms must be in a gas phase. This means that the substance has to be vaporised. Spectrum is studied in absorption or emission. UV spectroscopy All atoms absorb in the UV region because photons are energetic enough to excite outer electrons. If the frequency is high enough, Photoionisation takes place. Infra-red spectroscopy In Organic chemistry different types of interatomic bond vibrate at different frequencies in the infra-red part of the spectrum. The analysis of IR absorption spectra shows what type of bonds are present in the sample. Nuclear Magnetic Resonance spectroscopy NMR spectroscopy determines the different local environments of hydrogen or carbon atoms in an organic compound. This is used to determine the structure of the compound. Photoemission spectroscopy Less frequently used / combined spectroscopy See also
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