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

C Richard,P Groner,L Margulès,R A Motiyenko,J K Jørgensen,J.-C Guillemin

doi:10.1051/0004-6361/202141282

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.

Highlights

By May 2021, around 220 molecules have been detected in the interstellar medium (ISM) or circumstellar shells1
We present the first analysis of doubly deuterated dimethyl ether in its groundvibrational state, based on an effective Hamiltonian for an asymmetric rotor molecule with internal rotors
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

Summary

Introduction

By May 2021, around 220 molecules have been detected in the interstellar medium (ISM) or circumstellar shells. The asymmetric conformation is identified when one of the deuteriums is located on the C–O–C plane and the second is located in one of the other two locations This conformer has two equivalent configurations (a) and (b) in Fig. 1, with a possible tunneling effect between them as detected for some lines of the mono-deuterated species (Richard et al 2013). When both deuterium atoms are outside of the C–O–C plane, the conformation is called symmetric as it has a symmetry plane and belongs to the Cs symmetry point group. In the torsionalrotational part of the Hamiltonian, besides ρ, we determined the following parameters: β the angle between rho vector and principal axis a, ε10 the tunneling parameter representing the splitting between A and E symmetry sublevels, and two rotational constant tunneling parameters ([A − (B + C)/2]q=1 and [(B − C)/4]q=1)

Findings

Discussion

Conclusion