May 2007

Ketenimine

The discovery of interstellar ketenimine (CH2CNH) was reported in 2006 by Lovas et al. using the Green Bank Telescope, its eighth new detection in two years of operation. Ketenimine was found in Sgr B2, the richest known source of interstellar molecules in the galaxy. Two other isomers, methyl cyanide (CH3CN) and methyl isocyanide (CH3CN) have also been observed. Very tentative evidence has also been presented for cyclic 2H-azirine.

Ketenimine is both a specific compound and the group name for R1R2C=C=NR3 species containing the cumulenic C=C=N backbone and the =NR imine group. The C=C=N backbone is slightly non-linear in ketenimine.

There are a number of potential pathways to the formation of ketenimine under different interstellar conditions, most of which are noted by Lovas et al. It could possibly form by rearranging methyl cyanide or isocyanide, though both of these are endothermic processes with high barriers. The first spectroscopic characterization by Jacox & Milligan formed ketenimine in cold matrices with the acetylene + NH reaction, though this evidently has a small barrier in its entrance channel and requires a triplet to single intersystem crossing. The acetylene + NH2 reaction, chararacterized theoretically by Moskaleva & Lin, also has a small entrance channel barrier but yields ketenimine after a simple 1,2 H shift and elimination of a second H. Both might occur more efficiently in photolyzed ices.


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