Laboratory detection of a second carbon chain carbene - Butatrienylidene, H2CCCC

From laboratory measurement of 45 lines in its rotational spectrum, butatrienylidene, H2C4, has been identified, the second carbene with a known microwave spectrum in the sequence formed by the addition of successive carbon atoms to a linear cumulene backbone. With a dipole moment computed to be high (4.5 D), H2C4 is a good candidate for interstellar and circumstellar detection. This paper presents a determination of the rotational and leading centrifugal distortion constants and a tabulation of possible astronomical lines in the radio and far-IR.