November 2005

Propadienylidene

The linear isomer of C3H2 was first detected by Cernicharo et al. in 1991 in Taurus Molecular Cloud 1 (TMC-1), the closest known region of low-mass star formation.

Like the cyclic isomer, the linear form of C3H2 is a carbene species, where the terminal carbon has fewer bonds than the optimal four that carbon generally possesses. It is also a cumulene molecule by virtual of its pair of aligned and adjacent double bonds. Cumulenes have a -C=C(=C)n- backbone.

The l-C3H2 is slightly less stable energetically than the cyclic form. There are other isomers as well, including quasi-linear HCCCH and other cylic arrangements. None of the other structures have been observed in the ISM.


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