Definitions

formyl radical

List of molecules in interstellar space

This is a list of molecules that have been detected in the interstellar medium, grouped by the number of component atoms. The chemical formula is listed for each detected compound, along with any ionized form that has also been observed.

Detection

The molecules listed below were detected by spectroscopy. Their spectral features are generated by transitions of component electrons between different energy levels, or by rotational or vibrational spectra. Detection usually occurs in radio, microwave, or infrared portions of the spectrum. The first such molecule to be detected in the interstellar medium was the methylidyne radical (CH) in 1937.

Interstellar molecules are formed by chemical reactions within very sparse interstellar or circumstellar clouds of dust and gas. Usually this occurs when a molecule becomes ionized, often as the result of an interaction with a cosmic ray. This positively-charged molecule then draws in a nearby reactant by electrostatic attraction of the neutral molecule's electrons. Molecules can also be generated by reactions between neutral atoms and molecules, although this process is generally slower.

A particularly large and rich region for detecting interstellar molecules is Sagittarius B2 (Sgr B2). This giant molecular cloud lies near the center of the Milky Way galaxy and is a frequent target for new searches. About half of the molecules listed below were first found near Sgr B2, and nearly every other molecule has since been detected in this feature.

Molecules

The following tables list molecules that have been detected in the interstellar medium, grouped by the number of component atoms. If there is no entry in the Molecule column, only the ionized form has been detected. For molecules where no designation was given in the scientific literature, that field is left empty.

Diatomic

Molecule Designation Ions
AlCl Aluminium monochloride
AlF Aluminium monofluoride
C2 Carbon dimer
Fluoromethylidynium CF+
CH Methylidyne radical CH+
CN Cyanogen radical — CO Carbon monoxide CO+ CP Carbon monophosphide — CS Carbon monosulfide — FeO Iron(II) oxide — H2 Molecular hydrogen — HCl Hydrogen chloride — HF Hydrogen fluoride — HN Nitrogen monohydride — HO Hydroxyl radical — KCl Potassium chloride — N2 Molecular nitrogen — NO Nitric oxide — NS Nitrogen sulfide — NaCl Sodium chloride — O2 Molecular oxygen — PN Phosphorus nitride — PO Phosphorus monoxide — SH Sulfur hydride SH+ SO Sulfur monoxide SO+ SiC Carborundum — SiN Silicon mononitride — SiO Silicon monoxide — SiS Silicon monosulfide

Triatomic

Molecule Designation Ions
AlNC Aluminum isocyanide
C3 Tricarbon
C2H Ethynyl radical
C2O Dicarbon monoxide
C2S Thioxoethenylidene
C2P
CO2 Carbon dioxide
Protonated molecular hydrogen H3+
H2C Methylene
H2O Water
H2S Hydrogen sulfide
HCN Hydrogen cyanide
HCO Formyl radical HCO+
HCP Phosphaethyne
Thioformyl HCS+
HNC Hydrogen isocyanide
Diazenylium HN2+
HNO Nitroxyl
Isoformyl HOC+
KCN Potassium cyanide
MgCN Magnesium cyanide
MgNC Magnesium isocyanide
NH2 Amino radical
N2H+
N2O Nitrous oxide
NaCN Sodium cyanide
OCS Carbonyl sulfide
SO2 Sulfur dioxide
c-SiC2 c-Silicon dicarbide
SiCN Silicon carbonitride
SiNC Silicon naphthalocyanine

Four atoms

Molecule Designation Ions
l-C3H Propynlidyne 
c-C3H Cyclopropynylidyne
C3N Cyanoethynyl C3N
C3O Tricarbon monoxide
C3S Tricarbonsulfide
Hydronium H3O+
C2H2 Acetylene
H2CN Methylene amidogen H2CN+
H2CO Formaldehyde
H2CS Thioformaldehyde
HCCN — 
Protonated hydrogen cyanide HCNH+
Protonated carbon dioxide HOCO+
HNCO Isocyanic acid
HNCS Isothiocyanic acid
NH3 Ammonia
SiC3 Silicon tricarbide 

Five atoms

Molecule Designation Ions
C5 — 
CH4 Methane
c-C3H2 Cyclopropenylidene
l-H2C3 Propadienylidene
H2CCN Cyanomethyl
H2C2O Ketene
H2CNH Methylenimine
Protonated formaldehyde H2COH+
C4H Butadiynyl C4H
HC3N Cyanoacetylene 
HCC-NC Isocyanoacetylene
HCOOH Formic acid
NH2CN Cyanamide
HC(O)CN Cyanoformaldehyde
SiC4 Silicon-carbide cluster
SiH4 Silane

Six atoms

Molecule Designation Ions
c-H2C3O Cyclopropenone
C2H4 Ethylene
CH3CN Acetonitrile
CH3NC Methyl isocyanide
CH3OH Methanol
CH3SH Methanethiol
l-H2C4 — 
Protonated cyanoacetylene HC3NH+
HCONH2 Formamide
C5H Pentynylidyne
HC2CHO Propynal
HC4N — 
CH2CNH Ketenimine

Seven atoms

Molecule Designation Ions
c-C2H4O Ethylene oxide
CH3C2H Methylacetylene
H3CNH2 Methylamine
CH2CHCN Acrylonitrile
H2CHCOH Vinyl alcohol
C6H Hexatriynyl C6H
HC4CN Cyanodiacetylene
CH3CHO Acetaldehyde

Eight atoms

Molecule Designation
H3CC2CN Methylcyanoacetylene
H2COHCHO Glycolaldehyde
HCOOCH3 Methyl formate
CH3COOH Acetic acid
H2C6 Hexapentaenylidene
CH2CHCHO Propenal
CH2CCHCN Cyanoallene
C7H Heptatrienyl radical
NH2CH2CN Amino acetonitrile

Nine atoms

Molecule Designation Ions
CH3C4H Methyldiacetylene
CH3OCH3 Dimethyl Ether
CH3CH2CN Propionitrile
CH3CONH2 Acetamide
CH3CH2OH Trans-Ethyl Alcohol
C8H Octatetraynyl C8H
HC6CN Cyanohexatriyne
HC7N Cyanotriacetylene 
CH3CHCH2 Propylene (propene) 

Ten or more atoms

Atoms Molecule Designation Ions
10 (CH3)2CO Acetone
10 CH3CH2CHO Propanal
10 CH3C5N Methyl-cyano-diacetylene
11 HC8CN Cyanotetra-acetylene
11 CH3C6H Methyltriacetylene
11 H3COC2H5 trans-ethyl methyl ether
12 CH3OC2H5 Trans-ethyl methyl ether
12 C6H6 Benzene
13 HC10CN Cyanodecapentayne
18 Naphthalene C10H8

Deuterated molecules

These molecules all contain a deuterium atom.
Molecule Designation
HD, H2D+ Deuterated molecular hydrogen
HDO, D2O Heavy water
DCN Hydrogen cyanide
DCO Formyl radical
DNC Hydrogen isocyanide
N2D+ — 
NH2D, NHD2, ND3 Ammonia
HDCO, D2CO Formaldehyde
CH2DCCH, CH3CCD Methylacetylene

Unconfirmed

The following molecules have been reported as detected in scientific literature, but they have not yet been confirmed through subsequent searches.

See also

References

External links

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Molecule Designation
H2NH2CCOOH Glycine
CO(CH2OH)2 1,3-dihydroxypropanone