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absorption spectrum:see spectrumspectrum,
arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass spectrograph).
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absorption spectrumA spectrum that is produced when electromagnetic radiation has been absorbed by matter. Typically, absorption spectra are produced when radiation from an incandescent source, i.e. radiation with a continuous spectrum, passes through cooler matter. Radiation is absorbed (i.e. its intensity is diminished) at selective wavelengths so that a pattern of very narrow dips or of wider troughs – i.e. absorption lines or bands – are superimposed on the continuous spectrum.
The wavelengths at which absorption occurs correspond to the energies required to cause transitions of the absorbing atoms or molecules from lower energy levels to higher levels. In the hydrogen atom, for example, absorption of a photon with the required energy results in a ‘jump’ of the electron from its normal orbit to one of higher energy (see hydrogen spectrum).
The absorption lines (or bands) of a star are produced when elements (or compounds) in the outermost layers of the star absorb radiation from a continuous distribution of wavelengths generated at a lower level in the star. Basically the same elements occur in stars. Since each element has a characteristic pattern of absorption lines for any particular temperature (and pressure) range, there are several different types of stellar spectra depending on the surface temperature of the star. See spectral types. See also emission spectrum.
the spectrum that results when optical or X-radiation is passed through a substance and is selectively absorbed.