Cyanoketene: the microwave spectrum and structure of an unstable molecule

The unstable molecule cyanoketene has been prepared by pyrolysis in a flow system, and the microwave spectra of five isotopic species, a- and b-type, have been measured in the frequency range from 8 to 40 GHz. Precise rotational constants and centrifugal distortion parameters up to the sixth order were obtained. The molecule has been shown to be planar, and a reliable structure was derived. Also the N-quadrupole coupling constants and the dipole moment components have been determined. The results could be a basis for interstellar spectroscopy of this molecule.