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

•We recorded the high-resolution infrared spectrum of di-deuterated diacetylene.•The spectrum was recorded by FTIR in the 450-1100 cm−1 range.•A global analysis of the measured wavenumbers was performed.•An extended set of spectroscopic parameters has been derived.

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 ν8 fundamental band, the ν6+ν9, ν7+ν8, and ν6+ν8 combination bands and the ν8+ν9−ν9 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 v3=1 and the v8=v9=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.