Accurate rest-frequencies of ketenimine (CH2CNH) at submillimetre wavelength

Context. 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. Aims. 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. Methods. 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 degrees. The spectrum was recorded in the frequency range 80-620 GHz with the detection of 150 transitions. Results. 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 N-14 nucleus, which were accounted for in the analysis. Conclusions. 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 1 sigma uncertainties that are lower than 0.1 km s(-1) in radial equivalent velocity.