A number of molecules have been detected in the interstellar medium, in circumstellar envelopes around evolved stars, and comae and tails of comets through observation of their microwave, infrared, or optical spectra. The following table gives the molecules and the particular isotopic species that have been reported so far. All species not footnoted otherwise are observed in interstellar clouds, while some are also found in comets and circumstellar clouds. The table was last updated through November 2021 and lists 276 molecules (518 isotopic forms). Information on structural bond lengths, angles, and configuration for many of the molecules listed here can be found in “Structure of Free Molecules in the Gas Phase” in Section 9. See Ref. 1 for transition frequencies reported for a typical molecular cloud and Ref. 2 for a discussion of comet observations. Laboratory measurements and predicted frequencies may be found in Refs. 3 and 4.
Column definitions for the table are as follows.
Column heading | Definition |
Mol. form. | Molecular formula of observed interstellar molecule; molecules are listed by molecular formula in Hill order* |
Name | Name of interstellar molecule |
Isotopic species | Specific isotopic species that have been observed so far; molecular formula for species are written in Hill order*; D refers to deuterium; l- before the isotopic species indicates a linear configuration, while c- indicates a cyclic molecule |
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Mol. form | Name | Isotopic species | Synonym |
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AlCl | Aluminum monochloride | Al35Cla | |
AlCl | Aluminum monochloride | Al37Cla | |
AlF | Aluminum monofluoride | AlFa | |
AlF | Aluminum monofluoride | 26AlFa | |
AlHO | Aluminum hydroxide | AlOHa | |
AlO | Aluminum monoxide | AlOa | |
ArH+ | Argonium | 36ArH+ | |
ArH+ | Argonium | 38ArH+ | |
CAlN | Aluminum isocyanide | AlNCa | |
CCaN | Calcium isocyanide | CaNCa | |
CF+ | Fluoromethyliumylidene | CF+ | |
CFeN | Iron cyanide | FeCN | |
CH | Methylidyne | CH | |
CH | Methylidyne | 13CH | |
CH+ | Methyliumylidene | CH+ | |
CH+ | Methyliumylidene | 13CH+ | |
CD+ | Methyliumylidene-d | CD+ | |
CHMgN | Magnesium hydride isocyanide | HMgNCa | |
CHN | Hydrogen cyanide | HCN | Hydrocyanic acid |
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