molecules

Molecules in Space

Note: Deuterium isotopic species are not given separately anymore.

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 September 2024, 322 molecules are listed in the section of interstellar or circumstellar molecules. Only few these are tentative or somewhat uncertain. On the other hand some molecules are still missing (mainly metal compounds outside stellar atmospheres) in the table. Thus, we recommend phrases such as “more than 320 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 74 including three tentative detections. More may have to be added. The list includes protonated acetylene, C2H3+, the first molecule detected in an extragalactic source, but not in a galactic source. The first species detected in an extragalactic but not galactic source is 34SH+ also in this peculiar foreground galaxy.

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
CH+ C3* c-C3H C5* C5H C6H CH3C3N CH3C4H CH3C5N HC9N c-C6H6* C60*
CH C2H l-C3H C4Hl-H2C4 CH2CHCN HC(O)OCH3 CH3CH2CN (CH3)2CO CH3C6H n-C3H7CN C70*
CN C2O C3N C4Si C2H4*CH3C2H CH3COOH (CH3)2O (CH2OH)2 C2H5OCHO i-C3H7CN C60+*
OH C2S C3O l-C3H2CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH3OC(O)CH3 C2H5OCH3 c-C6H5CN
CO CH2 C3S c-C3H2 CH3NC CH3CHO C6H2 HC7N CH3CHCH2O CH3C(O)CH2OH 1-c-C5H5CN HC11N
H2 HCN C2H2* H2CCN CH3OH CH3NH2 CH2OHCHO C8H CH3OCH2OH c-C5H6 2-c-C5H5CN 1-C10H7CN
SiO HCO NH3 CH4* CH3SH c-C2H4O l-HC6H* CH3C(O)NH2 c-C6H4 HOCH2CH2NH2 CH3C7N (?) 2-C10H7CN
CS HCO+ HCCN HC3N HC3NH+ H2CCHOH CH2CHCHO C8H H2CCCHC3N H2CCCHC4H n-C3H7OH c-C9H8
SO HCS+ HCNH+ HCCNC HCCCHO C6H CH2CCHCN C3H6 C2H5NCO C10H (2023) i-C3H7OH 1-c-C5H5CCH
SiS HOC+ HNCO HCOOH NH2CHO CH3NCO H2NCH2CN CH3CH2SH C2H5NH2 (?) H2C(CH)3CN (2023) (CH3)2C=CH2 (2023) 2-c-C5H5CCH
NS H2O HNCS H2CNH C5N HC5O CH3CHNH CH3NHCHO HC7NH+ c-C5H4CCH2
C2** H2S HOCO+ H2C2O l-HC4H* HOCH2CN CH3SiH3 HC7O E-CH3CHCHCN 2-C9H7CN
NO HNC H2CO H2NCN l-HC4N HCCCHNH H2NC(O)NH2 HCCCHCHCN Z-CH3CHCHCN C6H5CCH (2023)
HCl HNO H2CN HNC3 c-H2C3O HC4NC HCCCH2CN H2CCHC3N CH3C(CN)CH2 CH3OCH2CH2OH (2024)
NaCl MgCN H2CS SiH4* H2CCNH c-C3HCCH HC5NH+ H2CCCHCCH CH2CHCH2CN
KCl MgNC H3O+ H2COH+ C5N l-H2C5 CH2CHCCH HOCHCHCHO (2024) HOCH2C(O)NH2 (2023)
AlCl N2H+ c-SiC3 C4H HNCHCN MgC5N MgC6H HC7N+ (2024) CH3CH2CCH (2024)
AlF N2O CH3* HC(O)CN SiH3CN CH2C3N C2H3NH2 CH2(CCH)2 (2024
PN NaCN C3NHNCNH C5S NC4NH+ (2023) (CHOH)2
SiC OCS PH3 CH3O MgC4H MgC5N+ (2023) HC2(H)C4
CP SO2 HCNO NH4+ CH3CO+ HC5N+ (2024) C7N (2023)
NH c-SiC2 HOCN H2NCO+ C3H3 HNC5 (2024) CH3CHCO (2023)
SiN CO2* HSCN NCCNH+ H2C3S CH2(CN)2 (2024 MgC6H+ (2023)
SO+ NH2 H2O2 CH3Cl HCCCHS Z-(CH)2(CN)2 (2024
CO+ H3+(*) C3H+ MgC3N C5O
HF SiCN HMgNC NH2OH C5H+
SiH? AlNC HCCO HC3O+ HCCNCH+
FeO? SiNC CNCN HC3S+ c-C3C2H
O2 HCP HONO H2C2S HC4S
CF+ CCP MgC2H C4S HMgC3N (2023)
PO AlOH HCCS HC(O)SH MgC4H+ (2023)
AlO H2O+ HNCN HC(S)CN H2C3H+ (2023)
OH+ H2Cl+ H2NC HCCCO H2C3N (2023)
CN- KCN HCCS+ NaCCCN (2023) (HO)2CO (2023)
SH+ FeCN CH3+ (2023) MgC3N+ (2023) H2CNCN (2024)
SH HO2 HCNS (2024) HC3N+ (2024) NCHCCS (2024)
HCl+ TiO2 HOCS+ (2024) HC3S (2024)
TiO C2N HNSO (2024) NC3S (2024)
ArH+ Si2C
N2 HS2
NO+ HCS
NS+ HSC
HeH+ NCO
PO+ CaNC
SiP ? NCS
FeC (2023) MgC2
HSO (2023)
CaC2 (2024)

The year of the detection 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, and 1,3-dihydroxypropanone, aka dihydroxyacetone. 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 HC(O)OCH3 C60*(?)
H2* HCO+ HNCO CH2NH HC4H* CH3CHO (CH3)2O
CH C2H C2H2* NH2CN HC(O)NH2 C2H3CN
CS HNC H2CS? l-C3H2 CH3SH
CH+ N2H+ HOCO+ H2CCN
CN OCS c-C3H H2CCO
SO HCO H3O+ C4H
SiO H2S l-C3H HCOOH
CO+ SO2 C3N C2H3+ (2024)
NO HOC+ l-C3H+
NS C2S H2CN
NH H2O+ H2NC
OH+ HCS+
HF H2Cl+
SO+ NH2
ArH+
CF+
SH+
O2 (?)
PN
  • molecules.txt
  • Last modified: 2024/10/02 12:23
  • by mueller