Synthesis of interstellar 1,3,5-heptatriynylidyne, $C7H(XΠ2)$⁠, via the neutral-neutral reaction of ground state carbon atom, $C(P3)$⁠, with triacetylene, $HC6H$ $(XΣ1g+)$ Available to Purchase

The reaction of ground-state carbon atom with a polyyne, triacetylene $(HC6H)$ is investigated theoretically by combining ab initio calculations for predicting reaction paths, RRKM theory to yield rate constant for each path, and a modified Langevin model for estimating capturing cross sections. The isomerization and dissociation channels for each of the five collision complexes are characterized by utilizing the unrestricted B3LYP/6-311G(d,p) level of theory and the CCSD(T)/cc-pVTZ calculations. Navigating with the aid of RRKM rate constants through web of ab initio paths composed of 5 collision complexes, 108 intermediates, and 20 H-dissociated products, the most probable paths, reduced to around ten species at collision energies of 0 and 10 kcal/mol, respectively, are identified and adopted as the reaction mechanisms. The rate equations for the reaction mechanisms are solved numerically such that the evolutions of concentrations with time for all species involved are obtained and their lifetimes deduced. This study predicts that the five collision complexes, c1–c5, would produce a single final product, $C7H$ $(p1)+H$⁠, via the most stable intermediate, carbon chain $HC7H$ (i1); namely, $C+HC6H→HC7H→C7H+H$⁠. Our investigation indicates that the title reaction is efficient to form astronomically observed $C7H$ in cold molecular clouds, where a typical translational temperature is 10 K.