Millimeter wave spectroscopy of cyanoketene (NC–CH=C=O) and an observational search in the ISM

Abstract

Context. Ketene was detected in the interstellar medium (ISM) in 1977. Until now, only one derivative, the ketenyl radical, has been observed in this medium. Due to its large dipole moment value, cynaoketene is one of the best candidates for possible ketene derivative detection. Aims. To date, the measurements of the rotational spectra have been limited to 60 GHz. The extrapolation of the prediction in the millimeter wave domain is inaccurate and does not permit an unambiguous detection. Methods. The rotational spectra were re-investigated up to 330 GHz. Using the new prediction cyanoketene was sought after in a variety of astronomical sources: NGS 63341, SgrB2(N), and ASAI sources. Results. A total of 1594 transitions were newly assigned and fitted together with those from previous studies, reaching quantum numbers up to J = 82 and Ka = 24. Watson’s asymmetric top Hamiltonian in the Ir representation was used for the analysis; both reductions A and S were tested. Logically, the S reduction gave the best results confirming that the molecule is very close to the prolate limit. Cynaoketene was not found in ISM; upper limits to the column density were derived in each source.