Spectroscopy

Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency.

Physical quantity measured

The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an amount or intensity of something.

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• The intensity of emitted electromagnetic radiation and the amount of absorbed electromagnetic radiation are studied by electromagnetic spectroscopy (see also cross section).
• The amplitude of macroscopic vibrations is studied by acoustic spectroscopy and dynamic mechanical spectroscopy.
• Kinetic energy of particles is studied by electron energy loss spectroscopy and Auger electron spectroscopy (see also cross section).
• The mass-to-charge ratios of molecules and atoms are studied in mass spectrometry. A mass spectrometer does not measure the kinetic energy of particles - all particles have the same known kinetic energy (or an integer multiple thereof, depending on the charge) - so it is disputable whether this field strictly is a type of spectroscopy.
• The number of molecules or atoms or quantum-mechanical states to which the frequency or energy parameter applies. In this case the spectra is usually called cross section.