![]() ![]() Because the energy E of a photon (a quantum of light) is related to its frequency ν by the relation E = hν, where h is Planck’s constant, spectroscopy is actually the measure of the interaction of photons with matter as a function of the photon energy. Spectroscopic techniques are not confined to electromagnetic radiation, however. The table summarizes the electromagnetic spectrum over a frequency range of 16 orders of magnitude. Spectroscopy now covers a sizable fraction of the electromagnetic spectrum. Because of this sensitivity, the most accurate physical measurements have been frequency measurements. ![]() Frequency shifts as small as one part in 10 15 of the frequency being measured can be observed with ultrahigh resolution laser techniques. Certain types of microwave, optical, and gamma-ray spectroscopy are capable of measuring infinitesimal frequency shifts in narrow spectroscopic lines. ![]() Isotopes of the same element are virtually identical chemically.) Trace amounts of pollutants or contaminants are often detected most effectively by spectroscopic techniques. (Isotopes are all atoms of an element that have unequal mass but the same atomic number. Single atoms and even different isotopes of the same atom can be detected among 10 20 or more atoms of a different species. Spectroscopic techniques are extremely sensitive. Learn about the use of gamma-ray spectroscopy to identify the quarry that was the source of granite found in ancient Roman ruins See all videos for this article Optical spectroscopy is used routinely to identify the chemical composition of matter and to determine its physical structure. The constituents of distant stars, intergalactic molecules, and even the primordial abundance of the elements before the formation of the first stars can be determined by optical, radio, and X-ray spectroscopy. The internal structure of the proton and neutron and the state of the early universe up to the first thousandth of a second of its existence are being unraveled with spectroscopic techniques using high-energy particle accelerators. Microwave spectroscopy was used to discover the so-called three-degree blackbody radiation, the remnant of the big bang (i.e., the primeval explosion) from which the universe is thought to have originated ( see below Survey of optical spectroscopy: General principles: Applications). Radio-frequency spectroscopy of nuclei in a magnetic field has been employed in a medical technique called magnetic resonance imaging (MRI) to visualize the internal soft tissue of the body with unprecedented resolution. Spectroscopic techniques have been applied in virtually all technical fields of science and technology. Spectroscopy, as applied to high-energy collisions, has been a key tool in developing scientific understanding not only of the electromagnetic force but also of the strong and weak nuclear forces. Spectroscopic analysis has been crucial in the development of the most fundamental theories in physics, including quantum mechanics, the special and general theories of relativity, and quantum electrodynamics. More recently, the definition has been expanded to include the study of the interactions between particles such as electrons, protons, and ions, as well as their interaction with other particles as a function of their collision energy. Spectroscopy, study of the absorption and emission of light and other radiation by matter, as related to the dependence of these processes on the wavelength of the radiation.
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