Absorption spectroscopy

Absorption spectroscopy identifies or quantifies substances by measuring how much electromagnetic radiation they absorb at different wavelengths. Its spectra reveal characteristic transitions between energy levels in atoms or molecules.

Beer–Lambert law: A relation linking absorbance to concentration, optical path length, and a substance’s absorptivity. It converts measured absorbance into concentration when the sample and measurement satisfy its assumptions.
Electromagnetic spectrum: The full range of electromagnetic radiation, ordered by wavelength or frequency. Absorption measurements select wavelengths from this broad range.
Ultraviolet–visible spectroscopy: A technique that measures absorption of ultraviolet and visible light by atoms or molecules. It is widely used to quantify absorbing compounds in solution.
Emission spectroscopy: Spectroscopy that analyzes radiation emitted by matter as it loses energy. It detects photons released by excited matter rather than photons removed from a beam.
Absorbance: A logarithmic measure of how much light a sample removes from a beam at a given wavelength. Absorbance is the central measured quantity in many absorption experiments.
Photon: A quantum of electromagnetic radiation that carries energy proportional to its frequency. Absorption occurs when matter takes up photons with suitable energies.
Infrared spectroscopy: A technique that uses infrared radiation to probe molecular vibrations and chemical bonds. Its absorption bands help identify functional groups and compounds.
Raman spectroscopy: A technique that identifies molecular vibrations from inelastically scattered light. It probes vibrational structure through shifted scattered photons, not direct absorption.
Optical spectroscopy: The study of how matter interacts with ultraviolet, visible, and infrared radiation. Absorption spectroscopy is one way optical spectroscopy examines light–matter interactions.
Energy level: A discrete allowed energy state of an atom, molecule, or other quantum system. Spectral absorption reflects transitions between distinct energy levels.

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