Molecules in Space

Note: Deuterium isotopic species are given separately only if their method of detection is intrinsically different from that of pure hydrogen ones. We plan to modify this in the future to include them with all hydrogen species.

The documentations generally provide information on the detection of the respective molecules, including minor isotopic species, molecules in excited vibrational states, or different media in which the species has been detected as well as links to articles.

All molecules have been detected (also) by rotational spectroscopy in the radiofrequency to far-infrared regions unless indicated otherwise.

* indicates molecules that have been detected by their rotation-vibration spectrum,
** those detected by electronic spectroscopy only.

Transition metal molecules detected in atmospheres of stars by electronic spectroscopy are currently not included. We plan to create a new table in the not so distant future dealing with molecules in stellar atmospheres. In this context, the table of molecules detected in the interstellar medium (ISM) or circumstellar envelopes (CSE) of late type stars, will be split. In the case of some metal monoxides, emission features have been detected in optical or IR spectra. Most likely, this emission indicates a presence of these molecules in the circumstellar shell. Around one handful of molecules may have to be added.

Note: Questionable or rebuted detections have been omitted from the table. Some noteworthy cases are given below the table. Tentative detections, which have a reasonable chance to be correct, are indicated by “?”. Usually the number of observed transitions that are, at least, fairly free of overlap is small. Some detections that have been reported as secure ones are indicated by “(?)” because (partial) overlap of lines cannot be ruled at the moment or because the line list is somewhat small; obviously, there may be cases on the edge.

As the decision whether a molecule can be considered as detected frequently is a controversial one we refrain from stating an exact number of molecules as detected. As of April 2020, 218 molecules have been detected in the interstellar medium or circumstellar shells; eight of these are tentative, somewhat uncertain, or questionable detections. On the other hand some molecules are missing (mainly metal compounds outside stellar atmospheres) in the table, the number of molecules detected in the ISM or in CSEs at least 210. Thus, we recommend phrases such as “more than 200 molecules have been detected in the interstellar medium or circumstellar shells”. Two reported detections have been questioned seriously. Therefore, these are viewed currently as “probably not yet detected” – see below. They do not show up in the table anymore.

The number of molecules detected in extragalactic sources is 69 including three tentative detections. More may have to be added.

We welcome comments on this list!

2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 8 atoms 9 atoms 10 atoms 11 atoms 12 atoms >12 atoms
H2 C3* c-C3H C5* C5H C6H CH3C3N CH3C4H CH3C5N HC9N c-C6H6* C60*
AlFC2H l-C3H C4Hl-H2C4 CH2CHCNHC(O)OCH3 CH3CH2CN(CH3)2CO CH3C6Hn-C3H7CN C70*
AlCl C2O C3N C4Si C2H4*CH3C2H CH3COOH (CH3)2O (CH2OH)2 C2H5OCHO i-C3H7CN C60+*
C2** C2S C3O l-C3H2CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH3OC(O)CH3 C2H5OCH3 c-C6H5CN
CH CH2 C3S c-C3H2 CH3NC CH3CHO C6H2 HC7N CH3CHCH2O CH3C(O)CH2OH (2020)
CH+ HCN C2H2* H2CCN CH3OH CH3NH2 CH2OHCHO C8H CH3OCH2OH
CN HCO NH3 CH4* CH3SH c-C2H4O l-HC6H* CH3C(O)NH2
CO HCO+ HCCN HC3N HC3NH+ H2CCHOH (?) CH2CHCHO(?) C8H-
CO+ HCS+ HCNH+ HC2NC HC2CHO C6H- CH2CCHCN C3H6
CP HOC+ HNCO HCOOH NH2CHO CH3NCO H2NCH2CN CH3CH2SH(?)
SiC H2O HNCS H2CNH C5N HC5O CH3CHNH CH3NHCHO
HCl H2S HOCO+ H2C2O l-HC4H* HOCH2CN (2019) CH3SiH3 HC7O
KCl HNC H2CO H2NCN l-HC4N HCCCHNH (2020) H2NC(O)NH2 (2019)
NH HNO H2CN HNC3 c-H2C3O
NO MgCN H2CS SiH4* H2CCNH (?)
NS MgNC H3O+ H2COH+ C5N-
NaCl N2H+ c-SiC3 C4H- HNCHCN
OH N2O CH3* HC(O)CN SiH3CN
PN NaCN C3N-HNCNH C5S
SO OCS PH3 CH3O MgC4H (2019)
SO+ SO2 HCNO NH4+
SiN c-SiC2 HOCN H2NCO+
SiO CO2* HSCN NCCNH+
SiS NH2 H2O2 CH3Cl
CS H3+(*) C3H+ MgC3N (2019)
HF SiCN HMgNC NH2OH (2020)
HD AlNC HCCO
FeO? SiNC CNCN
O2 HCP HONO (2019)
CF+ CCP MgC2H (2019)
SiH? AlOH
PO H2O+
AlO H2Cl+
OH+ KCN
CN- FeCN
SH+ HO2
SH TiO2
HCl+ C2N
TiO Si2C
ArH+ HS2
N2 HCS
NO+? HSC
NS+ NCO
HeH+ (2019) CaNC (2019)

The year most relevant to the detection (including isotopic species or vibrationally excited states) is given for recent results — the past two to three years.

Currently, three molecules have been reported as detected whose detections have been questioned fairly convincingly in subsequent papers. These molecules are aminoacetic acid, H2NCH2COOH, aka glycine, 1,3-dihydroxypropanone, aka dihydroxyacetone, and cyanodecapentayne, HC11N. We consider these molecules as not yet detected.

The detection of SH by rovibrational spectroscopy of the S-type star R Andromedae has been omitted from this table as the molecule is present in the stellar atmosphere. It is hoped that a table of molecules in stellar atmospheres will be available in the not too distant future. Note, however, that the SH radical has recently been detected unambiguously in the ISM.

2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 8 atoms >8 atoms
OH H2O H2CO c-C3H2 CH3OH CH3CCH HC6H c-C6H6*
CO HCN NH3 HC3N CH3CN CH3NH2 C60*(?)
H2* HCO+ HNCO CH2NH HC4H* CH3CHO
CH C2H C2H2* NH2CN HC(O)NH2 C2H3CN (2020)
CS HNC H2CS? l-C3H2 CH3SH (2020)
CH+ N2H+ HOCO+ H2CCN
CN OCS c-C3H H2CCO
SO HCO H3O+ C4H
SiO H2S l-C3H HCOOH (2020)
CO+ SO2 C3N (2020)
NO HOC+ l-C3H+ (2020)
NS C2S H2CN (2020)
NH H2O+
OH+ HCS+
HF H2Cl+
SO+ NH2
ArH+
CF+
SH+
O2 (?) (2020)
  • molecules.txt
  • Last modified: 2020/09/22 15:23
  • by mueller