A theoretical study of the reaction of HCO+ with C2H2

A theoretical study was performed for the reaction of formyl cation and ace tylene to give C3H3+ + O in flames and C2H3+ (nonclassical) + CO, both in f lames and in interstellar clouds. The corresponding Potential Energy Surfac e (PES) was studied at the B3LYP/cc-pVTZ level of theory, and single-point calculations on the B3LYP geometries were carried out at the CCSD(T)/cc-pVT Z level. Our results display a route to propynal evolving energetically und er C2H3+ (nonclassical) + CO and, consequently, accessible in interstellar clouds conditions. This route connects the most stable C3H3O+ isomer (C2-pr otonated propadienone) with a species from which propynal may be produced i n a dissociative electron recombination reaction. The reaction channel to p roduce the C3H3+ + O evolves basically through two TSs and presents an endo thermicity of 63.9 kcal/mol at 2000 K. According to our Gibbs energy profil es, the C2-protonated propadienone is the most stable species at low-modera te temperatures and, consequently, could play a certain role in interstella r chemistry. On the contrary, in combustion chemistry conditions (2000 K) t he C2H3+ (nonclassical) + CO products are the most thermodynamically favore d species. (C) 2000 John Wiley & Sons, Inc.