The high-resolution infrared spectrum of fully deuterated diacetylene below 1000 cm-1

Diacetylene (HC4H) is the simplest polyyne and has been the subject of several studies related to technology, materials, supramolecular chemistry, non-linear optics. It has been detected in space and in the atmosphere of Titan. Moreover, it is a model species to test sophisticated ab initio calculations. In this paper we report the study of the infrared spectrum of the rare isotopologue DC4D below 1000 cm(-1). The experiment has been performed by high resolution Fourier transform infrared spectroscopy. The v(8) fundamental band, the v(6) + v(9), v(7) + v(8) and v(8) + v(8) combination bands and the v(8) + v(9) - v(9) hot band have been observed and analysed, providing a set of accurate spectroscopic parameters. A global fit has also been performed in order to take into account the anharmonic resonance between the v(3) = 1 and the v(8) = v(9) = 1 states. The final results obtained from the global fit show a good improvement in the spectroscopic parameters for both the upper and lower states.