Torsional-rotational spectrum of doubly deuterated dimethyl ether (CH3OCHD2): First ALMA detection in the interstellar medium

Context. In 2013, we published the first rotational analysis and detection of mono-deuterated dimethyl ether in the solar-type protostar IRAS 16293-2422 with the IRAM 30 m telescope. Dimethyl ether is one of the most abundant complex organic molecules in star-forming regions, and its D-to-H (D/H) ratios are important to understand its chemistry and trace the source history.Aims. We present the first analysis of doubly deuterated dimethyl ether (methoxy-d(2)-methane, 1,1-dideuteromethylether) in its ground-vibrational state, based on an effective Hamiltonian for an asymmetric rotor molecule with internal rotors. The analysis covers the frequency range 0.15-1.5 THz.Methods. The laboratory rotational spectrum of this species was measured between 150 and 1500 GHz with Lille's submillimeter spectrometer. For the astronomical detection, we used the Atacama Large Millimeter/submillimeter Array observations from the Protostellar Interferometric Line Survey.Results. New sets of spectroscopic parameters have been determined by a least squares fit with the ERHAM code for both symmetric and asymmetric conformers. As for the mono-deuterated species, these parameters have permitted the first identification in space of both conformers of a doubly deuterated dimethyl ether via detection near the B component of the Class 0 protostar IRAS 16293-2422.