A Combined Crossed Molecular Beam and ab Initio Study of the Reactions C2(X∑g+, a3Πu) + C2H4 → n-C4H3(XA‘) + H(2S1/2)

The reactions of the dicarbon cluster C 2 in the 1 ∑ g + singlet ground state and 3 Π u triplet state with the simplest alkene ethylene, C 2 H 4, were unraveled under single collision conditions using the crossed molecular beam method with mass spectrometric detection. Our experimental data revealed the presence of a C 2 versus H substitution pathway leading to C 4 H 3 isomer(s) via bound C 4 H 4 intermediates. The crossed beam results were combined with ab initio electronic structure calculations of the relevant stationary points which disclose that the formation of the n -C 4 H 3 (X 2 A‘) product can take place through different reaction pathways via three-and four-membered ring structures. Based on electronic structure and RRKM calculations, the cyclobutyne molecule in its triplet electronic state should be a key intermediate in the C 2 (a 3 Π u ) reaction.