Monday, October 22, 2007


Spectroscopy is the study of the interaction between radiation (electromagnetic radiation, or light, as well as particle radiation) and matter. Spectrometry is the measurement of these interactions and an instrument which performs such measurements is a spectrometer or spectrograph. A plot of the interaction is referred to as a spectrum.

Historically, spectroscopy referred to a branch of science in which visible light was used for the theoretical study of the structure of matter and for qualitative and quantitative analyses. Recently, however, the definition has broadened as new techniques have been developed that utilise not only visible light, but many other forms of radiation.

Spectroscopy is often used in physical and analytical chemistry for the identification of substances through the spectrum emitted from or absorbed by them. Spectroscopy is also heavily used in astronomy and remote sensing. Most large telescopes have spectrometers, which are used either to measure the chemical composition and physical properties of astronomical objects or to measure their velocities from the Doppler shift of their spectral lines.

Nature of radiation measured

The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an amount or intensity of something.
  • Electromagnetic spectroscopy involves interactions with electromagnetic radiation, or light. Ultraviolet-visible spectroscopy is an example.
  • Electronic spectroscopy involves interactions with electron beams. Auger spectroscopy involves inducing the Auger effect with an electron beam.
  • Mechanical spectroscopy involves interactions with macroscopic vibrations, such as phonons. An example is acoustic spectroscopy, involving sound waves.
  • Mass spectroscopy involves the interaction of charged species with magnetic and/or electric fields, giving rise to a mass spectrum. The term "mass spectroscopy" is deprecated in favour of mass spectrometry, for the technique is primarily a form of measurement, though it does produce a spectrum for observation.
Measurement process

Most spectroscopic methods are differentiated as either atomic or molecular based on whether or not they apply to atoms or molecules. Along with that distinction, they can be classified on the nature of their interaction:
  • Absorption spectroscopy uses the range of the electromagnetic spectra in which a substance absorbs. This includes atomic absorption spectroscopy and various molecular techniques, such as infrared spectroscopy in that region and nuclear magnetic resonance (NMR) spectroscopy in the radio region.
  • Emission spectroscopy uses the range of electromagnetic spectra in which a substance radiates (emits). The substance first must absorb energy. This energy can be from a variety of sources, which determines the name of the subsequent emission, like luminescence. Molecular luminescence techniques include spectrofluorimetry.
  • Scattering spectroscopy measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles. The scattering process is much faster than the absorption/emission process. One of the most useful applications of light scattering spectroscopy is Raman spectroscopy.
Interesting articles about spectroscopy

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