An Etymological Dictionary of Astronomy and Astrophysics
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Chemistry: Of, relating to, or containing the six-carbon ring typical of the benzene (C₆H₆) series and related organic groups.

M.E. aromatyk, from M.Fr. aromatique, from L. aromaticus, from Gk. aromatikos, from aroma "seasoning, sweet spice," of unknown origin.

An organic compound which contains benzene rings in its structure. The simplest is therefore benzene (C₆H₆). Aromatic compounds have a planar ring of atoms linked by alternate single and double bounds.

→ aromatic; → compound.

A family of strong infrared emission bands at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 μm which are widely observed in a large variety of objects, such as → H II regions, → reflection nebulae, → planetary nebulae, and the → diffuse interstellar medium of our galaxy and other galaxies. Solar system objects, such as carbonaceous → meteorites and → interplanetary dust particles are also known to display these features. They are suggested to be due to → polycyclic aromatic hydrocarbons.

→ aromatic; → infrared; → band.

1) Chemistry: A family of → organic molecules composed of carbon and hydrogen atoms (→ hydrocarbons) in which → carbon atoms appear in multiple loops (polycyclic) with strong chemical → bonds that exist between them (aromatic). PAHs are formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances like tobacco or charbroiled meat. As a pollutant, they are of concern because some compounds (benzo(a)pyrene) have been identified as tending to cause cancer.
2) Astro.: Strong → infrared emission features at 3.3, 6.2, 7.7, 8.6, and 11.2 microns, which are attributed to PAH molecules in the form of → dust grains with radii smaller than 10 Å. PAHs are common toward various sources characterized by a strong → ultraviolet radiation field (such as → active galaxies, → reflexion nebulae, → planetary nebulae, → H II regions). In particular, they trace the presence of → massive stars. The PAH features are thought to result from the fluorescent emission process of PAH molecules and ions excited by ultraviolet radiation of nearby stars. PAHs are likely produced by → photoevaporation of → very small grains.

→ poly-; → cyclic; → aromatic; → hydrocarbon.