Accurate ro-vibrational rest frequencies of DC4H at infrared and millimetre wavelengths

Context. Diacetylene, C4H2, has been identified in several astronomical environments through its infrared spectrum. In contrast, monodeuterated diacetylene (DC4H) has not been detected in space so far owing to the low isotopic abundance of deuterated species but also to the rather poor laboratory spectroscopic characterisation of this molecule. Aims. The aim of this work is to provide accurate spectroscopic parameters for DC4H to achieve reliable predictions for both its spectra at millimetre and infrared wavelengths. Methods. We studied the rotational spectrum of DC4H in the range 85–615 GHz by millimetre-wave spectroscopy and the infrared spectrum below 1000 cm−1 by high-resolution, Fourier-transform spectroscopy. Several pure rotational transitions were recorded in the ground state and in excited vibrational bending states. The three fundamental bands v6, v7, and v8 have been identified and assigned in the infrared spectrum. Results. The rotational transitions were analysed together with the infrared data in a global fit that produces very accurate rovibrational parameters. The observed frequencies and wavenumbers are reported to provide precise guidance for astronomical searches.