2014A&A...565A..66D

Imine compounds are thought to have a role in the interstellar formation of complex organic species, including pre-biotic molecules. Ketenimine (CH₂CNH) is one of the four imines discovered in space. It was identified in Sgr B2(N-LMH) through the detection of three rotational lines in absorption. We present an extensive laboratory study of the ground-state rotational spectrum of CH₂CNH at submillimetre wavelengths, aimed at obtaining accurate rest-frequencies for radio-astronomical searches. The investigation was carried out using a source-modulation microwave spectrometer equipped with a cell that is coupled to a pyrolysis apparatus working at 1000°. The spectrum was recorded in the frequency range 80-620GHz with the detection of 150 transitions. The newly measured transition frequencies were analysed with previously available microwave and far-infrared data, yielding accurate rotational constants of CH₂CNH, the complete sets of quartic and sextic centrifugal distortion constants, and three octic constants. Several transitions exhibit a hyperfine structure due to the quadrupole and spin-rotation couplings of the ¹⁴N nucleus, which were accounted for in the analysis. The determined spectroscopic constants allowed for the computation of a list of highly accurate rest-frequencies for astrophysical purposes in the submillimetre and THz region with 1σ uncertainties that are lower than 0.1km/s in radial equivalent velocity.