2015A&A...579A..46M

The acetaldehyde molecule is ubiquitous in the interstellar medium of our galaxy, and due to its dense and complex spectrum, large dipole moment, and several low-lying torsional states, acetaldehyde is considered to be a ``weed'' molecule for radio astronomy observations. Mono-¹³C acetaldehydes ¹³CH₃CHO and CH₃¹³CHO are likely to be identified in astronomical surveys, such as those available with the very sensitive ALMA telescope. Laboratory measurements and analysis of the millimeter and submillimeter-wave spectra are the prerequisites for the successful radioastronomical search for the new interstellar molecular species, as well as for new isotopologs of already detected interstellar molecules. In this context, to provide reliable predictions of ¹³CH₃CHO and CH₃¹³CHO spectra in millimeter and submillimeter wave ranges, we study rotational spectra of these species in the frequency range from 50 to 945 GHz. The spectra of mono-¹³C acetaldehydes were recorded using the spectrometer based on Schottky-diode frequencymultiplication chains in the Lille laboratory. The rotational spectra of ¹³CH₃CHO and CH₃¹³CHO molecules were analyzed using the Rho axis method. In the recorded spectra we have assigned 6884 for the ¹³CH₃CHO species and 6458 for CH₃¹³CHO species new rotational transitions belonging to the ground, first, and second excited torsional states. These measurements were fitted together with previously published data to the Hamiltonian models that use 91 and 87 parameters to achieve overall weighted rms deviations 0.88 for the ¹³CH₃CHO species and 0.95 for CH₃¹³CHO. On the basis of the new spectroscopic results, predictions of transition frequencies in the frequency range up to 1THz with J≤60 and K_a≤20 are presented for both isotopologs.