- The range of characteristic frequencies of electromagnetic radiation that are readily absorbed and emitted by an atom. The atomic spectrum is an effect of the quantized orbits of electrons around the atom. An electron can jump from one fixed orbital to another: if the orbital it jumps to has a higher energy, the electron must absorb a photon of a certain frequency; if it is of a lower energy, it must give off a photon of a certain frequency. The frequency depends on the difference in energy between the orbitals. Explaining this phenomenon was crucial to the development of quantum mechanics. The atomic spectrum of each chemical element is unique and is largely responsible for the color of matter. Atomic spectra can also be analyzed to determine the composition of objects, such as stars, that are far away. See more at orbital. See also spectrum.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.