Understanding the chemical dynamics of the reactions of dicarbon with 1-butyne, 2-butyne, and 1,2-butadiene – toward the formation of resonantly stabilized free radicals

Abstract

The reaction dynamics of the dicarbon radical C₂(a³Π_u/X¹Σ_g⁺) in the singlet and triplet state with C₄H₆ isomers 2-butyne, 1-butyne and 1,2-butadiene were investigated at collision energies of about 26 kJ mol⁻¹ using the crossed molecular beam technique and supported by ab initio and RRKM calculations. The reactions are all indirect, forming C₆H₆ complexes through barrierless additions by dicarbon on the triplet and singlet surfaces. Isomerization of the C₆H₆ reaction intermediate leads to product formation by hydrogen loss in a dicarbon–hydrogen atom exchange mechanism forming acyclic C₆H₅ reaction products through loose exit transition states in overall exoergic reactions.