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

¹ Dipartimento di Chimica “G. Ciamician”Università di Bologna, via F. Selmi 2, 40126 Bologna, Italy
e-mail: claudio.degliesposti@unibo.it; luca.dore@unibo.it
² Centro de Astronomia e Astrofísica, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal
e-mail: bizzocchi@oal.ul.pt

Received: 6 February 2014
Accepted: 20 March 2014

Abstract

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°. 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 ¹⁴N 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 1σ uncertainties that are lower than 0.1 km s^-1 in radial equivalent velocity.