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Conflatuman (talk | contribs) Second line of the intro has become overlong for comprehension on first reading, and O III identification is redundant as was included in first sentence. Redrafted. |
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In [[astronomy]] and [[atomic physics]], '''doubly ionized oxygen''' is the [[ion]] [[oxygen|O]]<sup>2+</sup> (also known as '''O III''' in [[spectroscopic notation]]). Its emission [[forbidden line]]s in the [[visible spectrum]] fall primarily at the wavelength 500.7 nm, and secondarily at 495.9 nm. Before spectra of oxygen ions became known, these lines once led to a spurious identification of the substance as a new [[chemical element]]. Concentrated levels of O III are found in [[diffuse nebula|diffuse]] and [[planetary nebula|planetary]] nebulae. Consequently, narrow [[Dichroic filter|band-pass filter]]s that isolate the 501 nm and 496 nm wavelengths of light, that correspond to [[green]]-[[turquoise (color)|turquoise]]-[[cyan]] [[spectral colors]], are useful in observing these objects, causing them to appear at higher contrast against the filtered and consequently blacker background of space (and possibly [[light pollution|light-polluted]] terrestrial atmosphere) where the frequencies of [O III] are much less pronounced.
These [[emission line]]s were first discovered in the spectra of planetary nebulae in the 1860s. At that time, they were thought to be due to a new element which was named ''[[nebulium]]''. In 1927, [[Ira Sprague Bowen]]
Permitted lines of O III lie in the Middle [[Ultraviolet]] band and are hence inaccessible to terrestrial astronomy.
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