THEORETICAL-STUDIES ON THE C2H-2 REACTION - MECHANISM FOR HCO+CO, HCCO+O AND CH+CO2 FORMATION(O)

The reaction of the ethynyl radical with molecular oxygen has been exa mined using density functional theory. Two major reaction routes are o pen to the chemically activated HCCOO adduct 1: dissociation to HCCO O 16 and formation of the thermodynamically most stable products HCO + CO 12. HCCOO 1 --> dioxirenyl 2 --> oxyrenyloxy 3 --> oxo-ketene 5 - -> HCO + CO 12 --> H + 2CO 15. The CCSD(T)/6-311 + + G(d,p)//B3LYP/6-3 11 + + G(d,p) energies of the respective rate controlling transition s tates, 1/16 and 1/2, indicate that the route leading to H + CO + CO sh ould dominate. Several other [C-2,H,O-2] isomers and other, minor path ways have also been characterised. The present study reveals this reac tion to be a capture-limited association-elimination reaction with a h igh and pressure-independent rate coefficient. (C) 1998 Elsevier Scien ce B.V. All rights reserved.