INTERSTELLAR & INTERPLANETARY MATTER A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z           HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site interstellar molecules GO TO LIST OF MOLECULES Introduction More than 140 different varieties of molecules have been found in the interstellar medium, ranging in complexity from molecular hydrogen (H2), which is also by far the commonest molecule in space, through other familiar ones, such as water, hydrogen cyanide (HCN), nitrous oxide or "laughing gas" (N2O), and ethanol (CH3CH2OH), to esoteric carbon-chains known as cyano-polyynes, the biggest known of which is HC11N. In addition, there is strong evidence for even larger aromatic (carbon-ringed) molecules called polycyclic aromatic hydrocarbons, or PAHs. Some molecules, such as HCO+, were not even known on Earth at the time of their detection in space. Because chemical bonds holding molecules together are sensitive to high-energy radiation and high temperatures, molecules are found in cool astronomical environments such as the dark interior of dense interstellar clouds and in expanding envelopes around dying red giants (and also in comets and planetary atmospheres). Most of the molecular material in our galaxy and elsewhere occurs in giant molecular clouds (GMCs). Within these, the greatest concentration and diversity of molecules are found in pockets, known as hot cores, near certain recently formed luminous stars. Hot cores are very compact (fractions of a light year), warm (a few hundred K, compared to 10 or 20K for the general interstellar gas), and dense (more than 106 hydrogen molecules per cm3) condensations with remarkably rich millimeter-wave emission-line spectra. They also show up as powerful infrared objects. The Orion Nebula contains two hot cores, which, being the nearest such objects, are also the most well-studied. Interstellar molecules are formed through a complicated network of chemical reactions in situ, inside the interstellar or circumstellar clouds where they are found. Crucial to their synthesis is the presence of dust grains. The icy surface of these grains both shields molecules from stellar ultraviolet that would otherwise disrupt the chemical bonds and provides a surface on which atoms, radicals, and molecules can congregate and interact. Laboratory studies have shown that not only simple molecules can be made in this way but elaborate molecules (yet to be detected in space) that may be important in the origin of life itself. Among the molecules of biochemical interest already detected in the Sagittarius B2 cloud, near the center of the Galaxy, is glycolaldehyde (C2H4O2), a simple sugar that can combine with other molecules to form the more complex sugars ribose and glucose. Ribose is a building block of nucleic acids such, as RNA and DNA, which carry the genetic code of living organisms. Observations also suggest the presence of glycine, the simplest amino acid (a chemical unit of proteins), in Sag B2. LIST OF KNOWN INTERSTELLAR MOLECULES Diatomic molecular species name discovery year CH methylidyne radical 1937 CN cyanogen radical 1940 CH+ methylidyne cation 1941 OH hydroxyl radical 1963 CO carbon monoxide 1970 H2 molecular hydrogen 1970 SiO silicon monoxide 1971 CS carbon monosulfide 1971 SO sulfur monoxide 1973 SiS silicon sulfide 1975 NS nitrogen sulfide 1975 C2 carbon dimer 1977 NO nitric oxide 1978 HCl hydrogen chloride 1985 NaCl sodium chloride 1987 AlCl aluminum (I) chloride 1987 KCl potassium chloride 1987 AlF aluminum (I) fluoride 1987 PN phosphorus nitride 1987 SiC silicon carbide 1989 CP   1990 NH   1991 SiN silicon nitride 1992 SO+ sulfur monoxide cation 1992 CO+ carbon monoxide cation 1993 HF hydrogen fluoride 1997 LiF lithium hydride 1998 SH   2000 FeO iron (II) oxide; 2002 N2 molecular nitrogen 2004 CF+   2006 O2 molecular oxygen 2007 Triatomic Molecular species Name Discovery year H2O water 1969 HCO+ formyl cation 1970 HCN hydrogen cyanide 1971 OCS carbonyl sulfide 1971 H2S hydrogen sulfide 1972 HNC hydrogen isocynaide 1973 N2H+ protated nitrogen ion 1974 C2H ethynyl radical 1974 SO2 sulfur dioxide 1975 HDO deuterated water 1975 HCO formyl radical 1976 HNO   1977 OCN-   1979 HCS+   1981 HOC+   1983 c-SiC2   1984 MgNC magnesium isocyanide 1986 C2S   1987 C3 carbon trimer 1987 CO2 carbon dioxide 1989 CH2   1989 C2O carbene 1991 NH2   1993 NaCN sodium cyanide 1994 N2O nitrous oxide 1994 MgCN magnesium cyanide 1995 H3+   1996 SiCN silicon cyanide 2000 AlNC aluminum isocynaide 2002 SiNC silicon isocyanide 2004 4-atomic Molecular species Name Discovery year NH3 ammonia 1968 H2CO formaldehyde 1969 HNCO isocyanic acid 1972 H2CS thioformaldehyde 1973 C3N cyanoethynyl 1977 HNCS isothiocyanic acid 1979 HOCO+ protonated carbon dioxide 1981 C3H propynlidyne radical 1985 C3O tricarbon monoxide 1985 HCNH+ protonated hydrogen cyanide 1986 H3O+ hydronium ion 1986 C3S tricarbon sulfide 1987 c-C3H cyclic propynlidyne radical 1987 C2H2 acetylene 1989 HC2N   1991 H2CN methylene amidogen 1994 SiC3 silicon tricarbide 1999 CH3   2000 5-atomic Molecular species Name Discovery year HC3N cyanoacetylene 1971 HCOOH formic acid 1971 CH2NH methylenimine 1973 NH2CN cyanamide 1975 H2C2O ketene 1977 C4H   1978 SiH4 silane 1984 c-C3H2 cyclopropenylidene 1985 CH2CN cyanomethyl radical 1988 C5   1989 SiC4 silicon tetracarbide 1989 l-C3H2 l-cyclopropenylidene 1991 CH4 methane 1991 HC2NC isocyanoacetylene 1992 HNC3   1992 H2COH+   1996 C4H-   2007 6-atomic Molecular species Name Discovery year CH3OH methanol 1970 CH3CN methyl cyanide 1971 NH2HCO formamide 1973 CH3CHO acetaldehyde 1973 C2H4 ethene 1983 C5H   1986 CH2CHO propynal 1988 HC3NH+   1994 C5N cyanobutadiynyl 1998 H2COH+   1996 C4H-   2007 C4H2 diacetylene 2001 HC4N   2004 c-C2H3O cyclopropenone 2006 CH2CNH ketenimine 2006 7-atomic Molecular species Name Discovery year CH3NH2 methylamine 1974 CH2CHCN acrylonitrile 1975 CH3C2H methlacetylene 1973 HC5N cyanodiacetylene 1978 C6H hexatriynyl 1986 c-C2H4O ethylene oxide 1997 CH2CHOH vinyl alcohol 2001 C6H-   2006 8-atomic Molecular species Name Discovery year CH3C3N methylcyanoacetylene 1984 C7H  methylamine 1997 CH3COOH acetic acid 1997 CH2OHCHO glycoaldehyde 2000 C6H2 triacetylene 2001 CH2CHCHO propenal 2004 CH2CCHCN cyanoallene 2006 9-atomic Molecular species Name Discovery year CH3OCH3 dimethyl ether 1974 C2H5OH trans-ethanol 1975 CH3CH2CN propionitrile (ethyl cyanide) 1977 HC7N cyanohexatriyne (cyanotriacetylene) 1978 CH3C4H methyldiacetylene 1984 C8H   1996 CH3CONH2 acetamide 2006 10-atomic Molecular species Name Discovery year (CH3)2CO acetone 1987 NH2CH2COOH glycine 2003 CH3CH2CHO propanal 2004 CH3C5N methylcyanodiacetylene 2006 11-atomic Molecular species Name Discovery year HC9N cyanotetra-acetylene 1978 HOCHC2CH2OH ethylene glycol 2002 CH3C6H methyltriacetylene 2006 12-atomic Molecular species Name Discovery year C6H6 benzene 2001 CO(CH2OH)2 1,3 dihydroxyacetone 2005 13-atomic Molecular species Name Discovery year HC11N cyanodecapentayne 1997 Related categories    • ASTROBIOLOGY    • INTERSTELLAR AND INTERPLANETARY MATTER Archived news And now antifreeze in space (Apr 21, 2002) Vinyl alcohol molecules found in space (Oct 6, 2001) Benzene found in interstellar space (Jan 23, 2001) Sweet news for astrobiologists (Jun 18, 2000) External site Current listing of all known interstellar molecules Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP