Directed gas phase preparation of ethynylallene (HCCCHCCH; XA') the crossed molecular beam reaction of the methylidyne radical (CH; XΠ) with vinylacetylene (HCCHCCH; XA').

The gas-phase bimolecular reaction of the methylidyne (CH; XΠ) radical with vinylacetylene (HCCHCCH; XA') was conducted at a collision energy of 20.3 kJ mol under single collision conditions exploiting the crossed molecular beam experimental results merged with electronic structure calculations and molecular dynamics (AIMD) simulations. The laboratory data reveal that the bimolecular reaction proceeds barrierlessly indirect scattering dynamics through long-lived CH reaction intermediate(s) ultimately dissociating to CH isomers along with atomic hydrogen with the latter predominantly originating from the vinylacetylene reactant as confirmed by the isotopic substitution experiments in the D1-methylidyne-vinylacetylene reaction. Combined with calculations of the potential energy surface (PES) and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations, the experimental determined reaction energy of -146 ± 26 kJ mol along with the distribution minimum of () at 90° and isotopic substitution experiments suggest ethynylallene (p1; Δ = -230 ± 4 kJ mol) as the dominant product. The ethynylallene (p1) may be formed with extensive rovibrational excitation, which would result in a lower maximum translational energy. Further, AIMD simulations reveal that the reaction dynamics leads to p1 (ethynylallene, 75%) plus atomic hydrogen with the dominant initial complex being i1 formed by methylidyne radical addition to the double CC bond in vinylacetylene. Overall, combining the crossed molecular beam experimental results with electronic structure calculations and molecular dynamics (AIMD) simulations, ethynylallene (p1) is expected to represent the dominant product in the reaction of the methylidyne (CH; XΠ) radical with vinylacetylene (HCCHCCH; XA').