Absorption spectrum

An absorption spectrum shows how strongly a substance absorbs light at different wavelengths. Its pattern of peaks and bands reflects the substance’s interaction with light.

Beer–Lambert law: A relation connecting light absorbance to a substance’s concentration and the distance light travels through it. It explains how measured absorbance changes with concentration and sample path length.
UV–visible spectroscopy: A technique that measures a sample’s absorption of ultraviolet and visible light. It uses absorption spectra to analyze electronic transitions and sample composition.
Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by frequency or wavelength. An absorption spectrum samples a portion of this continuous range.
Emission spectrum: A graph showing the wavelengths and intensities of light emitted by a source. It records light released by a substance, rather than wavelengths removed from an incident beam.
Electronic transition: A change in an atom or molecule’s electronic state after absorbing or emitting energy. Many ultraviolet and visible absorption bands arise from transitions between electronic states.
Infrared spectroscopy: A technique that measures infrared absorption to identify molecular vibrations and chemical bonds. Its spectra use absorption bands to help identify molecular structures.
Photon: A quantum of electromagnetic radiation that carries energy and momentum. Absorption occurs when a photon supplies energy allowed by the absorbing substance.
Action spectrum: A graph showing how the effectiveness of light varies with wavelength in producing a measured biological response. It tracks biological effect, which need not match the amount of light absorbed.
Vibrational spectroscopy: Methods that probe molecular vibrations by measuring interactions with infrared or Raman light. Infrared absorption spectra often reveal molecular vibrational modes.
Atomic absorption spectroscopy: An analytical method that determines elemental concentrations by measuring light absorbed by free atoms. Element-specific absorption lines provide a basis for measuring trace metals.

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