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.