Definition of absorption spectrum

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Photonics Dictionary

absorption spectrum: An absorption spectrum is a graphical representation of the absorption of light by a material as a function of wavelength, frequency, or energy. It displays the specific wavelengths of light that are absorbed by the atoms or molecules of a substance, revealing information about the material's composition and structure.

Formation: An absorption spectrum is produced when light passes through a sample, and certain wavelengths are absorbed by the material. The absorbed wavelengths correspond to the energy differences between specific energy levels of the atoms or molecules in the material.

Appearance: The absorption spectrum appears as a series of dark lines or bands on a bright continuous background when viewed with a spectroscope. Each dark line represents a wavelength at which light is absorbed.

Types of transitions:

Electronic transitions: Absorption of light that promotes electrons to higher energy levels, typically seen in the ultraviolet and visible regions of the spectrum.

Vibrational transitions: Absorption of light that increases the vibrational energy of molecules, typically observed in the infrared region.

Rotational transitions: Absorption of light that increases the rotational energy of molecules, typically seen in the microwave region.

Characteristic lines: Each element or compound has a unique absorption spectrum with characteristic lines or bands, acting as a fingerprint for identifying the substance.

Applications:

Chemical analysis: Identifying and quantifying substances in a mixture.

Astronomy: Determining the composition, temperature, and motion of celestial objects by analyzing the absorption spectra of stars and galaxies.

Environmental science: Monitoring pollutants and analyzing atmospheric gases.

Material science: Studying the optical properties of materials and coatings.

Continuous and line spectra:

Continuous spectrum: A smooth range of wavelengths without any interruptions, typically seen in the emission spectrum of a hot, dense object.

Line spectrum: A series of discrete lines or bands, each corresponding to a specific wavelength of absorbed light, typical of gaseous substances.

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