Laboratory detection of propadienylidene, H2CCC

Abstract

From laboratory measurement of more than 50 lines of its rotational spectrum, propadienylidene, H2CCC, a highly polar carbene and the lowest energy isomer of a readily observed interstellar molecule, the cyclopropenylidene ring c-C3H2, has been identified for the first time in the gas phase. The rotational and centrifugal distortion constants of H2CCC have been determined to sufficient accuracy to predict frequencies of the astronomically interesting lines in the radio spectrum to an uncertainty of 0.1 km/s or better. Propadienylidene is now an excellent candidate for interstellar and circumstellar detection; if found, it would be of interest as one of only a few known interstellar isomers and the first of a predicted series of highly polar cumulene carbenes.