Molecules in Space

ISM/CSS
extragalactic molecules

Press release by the MPIfR on the radio astronomical detection of titanium monoxide (TiO) and titanium dioxide (TiO₂) in the circumstellar envelope of the read super giant VY Canis Majoris. Deutsche Version der Pressemitteilung.

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 March 2013, at least 175 molecules have been detected unambiguously in the interstellar medium or circumstellar shells; four of these are tentative detections, and for currently three, the situation may be somewhat uncertain. Including some molecules missing in the table, the number of molecules detected in the ISM or in CSEs is around 180. Thus, we recommend phrases such as "around 180 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 55 plus 1 tentative plus 1 questionable detections. More may have to be added.

We welcome comments on this list !