Laboratory rotational spectra of the dimethyl ether ¹³C-isotopologues up to 1.5 THz^⋆

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: koerber@ph1.uni-koeln.de
² Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
³ Centre for Star and Planet Formation, Niels Bohr Institute, Juliane Mariesvej 30, 2100 Copenhagen Ø., Denmark
⁴ Institut für Anorganische Chemie, Universität zu Köln, Greinstr. 6, 50939 Köln, Germany

Received: 15 May 2013
Accepted: 29 August 2013

Abstract

Context. Dimethyl ether is found in high abundance in the interstellar medium. Owing to its strong and dense spectrum throughout the entire microwave and terahertz regime, it contributes to the spectral confusion in astronomical line surveys. The great sensitivity of new observatories like ALMA enhances the need for reliable spectroscopic data, especially for isotopic species of abundant molecules. In addition, the study of the interstellar ¹²C/¹³C isotopic ratio can be used as a tracer of the formation process of a molecular species, and thus it gives insight into the chemical evolution of the observed region.

Aims. The interpretation of astronomical observations depends on the knowledge of accurate rest frequencies and intensities. The objective of this work is to provide spectroscopic data for the two ¹³C-isotopologues of dimethyl ether in the vibrational ground state.

Methods. High-resolution rotational-torsional spectra of ¹²CH₃O¹³CH₃ and (¹³CH₃)₂O have been measured in the laboratory covering frequencies up to 1.5 THz. The analysis is based on an effective rotational Hamiltonian for molecules with two large-amplitude motions.

Results. Predictions of the complete ground state rotational spectrum of dimethyl ether-¹³C₁ and -¹³C₂ up to 2 THz are presented with accuracies better than 1 MHz. Based on the laboratory work, transitions of ¹²CH₃O¹³CH₃ dimethyl ether have been detected for the first time in a large submillimeter line survey of the high-mass star forming region G327.3-0.6 performed with the APEX telescope.