October 2009


Butatrienylidene (H2C4) was discovered in 1991 in the circumstellar shell of IRC + 10216 by Cernicharo et al. using the IRAM 30m radiotelescope using experimental spectra of the species measured by Killian et al. Subsequent detections include dense molecular cloud TMC-1 by Kawaguchi et al. in 1991 and toward the low-mass protostar IRAS 04368+2557 in L1527 by Sakai et al. in 2008.

The H2Cn species are known as cumulene carbenes. For an even number of carbon atoms, they are much less stable than their acetylenic counterparts, HCnH, in the case of of butatrienylidene, diacetylene. However, where the acetylenic compounds have no permanent dipole moments, the cumulene carbons have very large dipole moments and therefore have intense rotational spectra.

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