Here is an example of how difficult identifying molecules can be in the interstellar medium and even in circumstellar envelopes. It turns out that C4H and H2CCCC have transitions that exactly coincide with those of methanol (see below). These are more likely the correct assignments. Yet, our paper was destined to be printed. An erratum has been published with the correct identifications given.
Ah, such is science at the edge. Sometimes you have to risk being wrong, just in case you are right.
Latter, W. B. and Charnley, S. B. 1996, ApJ
Letters, 463, L37.
Erratum: 1996, Astrophysical Journal Letters, 465, L81.
S. B. Charnley
U.C. Berkeley and NASA/Ames Research Center
In The Astrophysical Journal Letters
Millimeter-wave observations of the extremely carbon-rich circumstellar envelope around the mass losing star IRC+10216 show several emission lines that we identify with rotational transitions of methanol (``wood alcohol''; CH3OH). In our paper (Latter & Charnley 1996, ApJ Letters, in press), we describe our observations and the reasoning leading to this identification. We argue that shock chemistry, ion-molecule reactions, and grain surface reactions might all be potential sources of circumstellar methanol. Each of these pathways either require or produce water in the envelope of IRC+10216. Water (H2O) is another unexpected component in this type of environment. It is also very difficult to observe from within the Earth's atmosphere. This important prediction of the presence of water must await space-based infrared or millimeter/submillimeter-wave observations.
This detection of methanol remains tentative because other transitions were not found, perhaps due to unusual excitation in the circumstellar envelope, or to insufficient sensitivity. A systematic and sensitive line search is required. The presence of methanol in a C-rich circumstellar envelope is unexpected and, if confirmed, will have a far-reaching impact on our understanding of circumstellar chemistry.
Subject headings: molecular processes -- stars: circumstellar matter -- stars: late-type -- stars: carbon
See the Erratum here.