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

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 C-12/C-13 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 C-13-isotopologues of dimethyl ether in the vibrational ground state. Methods. High-resolution rotational-torsional spectra of (CH3OCH3)-C-12-C-13 and ((CH3)-C-13)(2)O 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-C-13(1) and -C-13(2) up to 2 THz are presented with accuracies better than 1 MHz. Based on the laboratory work, transitions of (CH3OCH3)-C-12-C-13 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