Torsional-rotational spectrum of doubly deuterated dimethyl ether (CH3OCHD2)

Abstract

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-d2-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.