ON THE FORMATION OF ORTHO-BENZYNE (o-C6H4) UNDER SINGLE COLLISION CONDITIONS AND ITS ROLE IN INTERSTELLAR CHEMISTRY

The elementary reaction of the D1-ethynyl radical (C2D) with vinylacetylene (C4H4) was studied under single collision conditions via crossed molecular beam experiments and electronic structure calculations. The results suggested that besides two acyclic isomers as predicted computationally, the ortho-benzyne (o-C6H4)-in its singly deuterated form-which is considered as an important intermediate in the formation of polycyclic aromatic hydrocarbons, can be formed in this process. This reaction was carried out at a collision energy of 40.9 kJ mol(-1), which is roughly equal to about 4000 K as present in photospheres of carbon stars and protoplanetary nebulae close to the central star. As the reaction is exoergic and involves no barriers higher than the separated reactants, our findings suggest that ortho-benzyne can also be formed in molecular clouds like TMC-1.