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A closely spaced structure of the spectrum lines forming a multiplet component in the spectrum of an atom or molecule, or of a liquid or solid. In the emission spectrum for an atom, when a multiplet component is examined at the highest resolution, this component may be seen to be resolved, or split, into a group of spectrum lines which are extremely close together. This hyperfine structure may be due to a nuclear isotope effect, to effects related to nuclear spin, or to both. See Isotope shift, Spin (quantum mechanics)
The measurement of a hyperfine structure spectrum for a gaseous atomic or molecular system can lead to information about the nuclear magnetic and quadrupole moments, and about the atomic or molecular electron configuration. Important methods for the measurement of hyperfine structure for gaseous systems may employ an interferometer, or use atomic beams, electron spin resonance, or nuclear spin resonance.
the splitting of atomic energy levels into closely spaced sublevels as a result of the interaction of the nuclear magnetic moment with the magnetic field of the atomic electrons. The energy δE of this interaction depends on the possible relative orientations of the nuclear spin and the electron spins. The number of these orientations determines the number of components of the hyperfine structure. Energy levels can also be split and shifted as a result of the interaction of the nuclear quadrupole moment with the electric field of the electrons.
The spacing between fine structure sublevels is 1,000 times greater than the spacing between hyperfine structure sublevels, since the energy of the spin-orbit interaction is 1,000 times greater than δE. Because of the hyperfine splitting of levels, an atomic spectrum exhibits instead of a single spectral line a group of closely spaced lines called the hyperfine structure in the spectral line.
The hyperfine structure in a spectral line can be complicated by isotope shifts—that is, by differences in the frequencies of the spectral lines of the isotopes of an element. In this case, there occurs a superposition of the spectra of the various isotopes of the element. For heavy elements, isotope shifts are of the same order of magnitude as δE.
Hyperfine structure can also be observed in the spectra of molecules and crystals.
REFERENCESShpol’skii, E. V. Atomnaia fizika, 6th ed., vol. I. Moscow, 1974.
Frish, S. E. Oplicheskie spektry atomov. Moscow-Leningrad, 1963.
Frish, S. E. Speklroskopicheskoe opredelenie iadernykh momentov. Leningrad-Moscow, 1948.