A crossed beams and ab initio investigation on the formation of cyanodiacetylene in the reaction of cyano radicals with diacetylene.

The crossed molecular beams reaction of ground state cyano radicals (CN) with diacetylene (HCCCCH) was studied in the laboratory under single collision conditions. Combining the derived center-of-mass translational energy and angular distributions with novel electronic structure calculations, we show that the linear cyanodiacetylene molecule (HCCCCCN) is the sole reaction product. Our study provided no substantiation of two alternative products which have been suggested previously: cyanoacetylene (HCCCN), speculated to be synthesized via the exchange of the ethynyl by the cyano group, and the 1,3-butadiynyl radical (HCCCC), thought to be formed via hydrogen abstraction. The unambiguous identification of cyanodiacetylene formed in an exoergic, barrierless bimolecular reaction of the cyano radical with diacetylene strongly suggests that cyanodiacetylene can be also synthesized via this process in the interstellar medium (cold molecular clouds) and in hydrocarbon-rich atmospheres of planets and their moons such as Titan.