Branch of analysis devoted to identifying elements and compounds and elucidating atomic and molecular structure by measuring the radiant energy absorbed or emitted by a substance at characteristic wavelengths of the electromagnetic spectrum (including gamma ray, X-ray, ultraviolet, visible light, infrared, microwave, and radio-frequency radiation) on excitation by an external energy source. The instruments used are spectroscopes (for direct visual observation) or spectrographs (for recording spectra). Experiments involve a light source, a prism or grating to form the spectrum, detectors (visual, photoelectric, radiometric, or photographic) for observing or recording its details, devices for measuring wavelengths and intensities, and interpretation of the measured quantities to identify chemicals or give clues to the structure of atoms and molecules. Helium, cesium, and rubidium were discovered in the mid-19th century by spectroscopy of the Sun's spectrum. Specialized techniques include Raman spectroscopy (see Chandrasekhara Venkata Raman), nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), dynamic reflectance spectroscopy, microwave and gamma ray spectroscopy, and electron spin resonance (ESR). Spectroscopy now also includes the study of particles (e.g., electrons, ions) that have been sorted or otherwise differentiated into a spectrum as a function of some property (such as energy or mass). Seealso mass spectrometry; spectrometer; spectrophotometry.
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Analytic technique by which chemical substances are identified by sorting gaseous ions by mass using electric and magnetic fields. A mass spectrometer uses electrical means to detect the sorted ions, while a mass spectrograph uses photographic or other nonelectrical means; either device is a mass spectroscope. The process is widely used to measure masses and relative abundances of different isotopes, to analyze products of a separation by liquid or gas chromatography, to test vacuum integrity in high-vacuum equipment, and to measure the geological age of minerals.
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On 5 October 2006 NASA announced the results of research using the Japanese JAXA Suzaku satellite, after earlier work with the XMM-Newton satellite. "The observations include clocking the speed of a black hole's spin rate and measuring the angle at which matter pours into the void, as well as evidence for a wall of X-ray light pulled back and flattened by gravity." The study teams observed X ray emissions from the "broad iron K line" near the event horizon of several super-massive black holes of galaxies called MCG-6-30-15 and MCG-5-23-16. The normally narrow K-line is broadened by the doppler shift (red shift or blue shift) of the X ray light emitted by matter being affected by the gravity of the black hole. The results coincide with predictions Einstein's theory of general relativity. The teams were led by Andrew Fabian of Cambridge University, England, and James Reeves of NASA's Goddard Space Flight Center, Greenbelt, Maryland, United States.