Guided-ion beam study of the O-2(+)+C2H2 charge-transfer and chemical reaction channels

Guided-ion beam cross section and product ion time-of-flight (TOF) measurem ents are presented for the O-2(+)((2)Pi(g)) + C2H2 reaction over the center -of-mass collision energy range of 0.05-12 eV. The reaction exhibits a stro ng charge-transfer (CT) channel and several weak chemical reaction channels leading to the following product ions: C2H2O+, CH2+, COH+/HCO+, CO+, CH+, and C+. The magnitude of the charge-transfer cross section is comparable to the capture cross section at low collision energies. The charge-transfer p roducts are characterized predominantly by a direct, long-range mechanism t hat is accompanied by smaller impact parameter collisions involving longer- lived complexes, whose lifetimes are several times shorter than the complex rotational period. The TOF analysis indicates that the complexes also deca y to chemical reaction products at higher energies. A density functional su rvey of intermediates is conducted. The chemical reaction products are post ulated to be formed via an endothermic transition state associated with a H 2CCO2+ intermediate. (C) 1999 American Institute of Physics. [S0021-9606(99 )00309-8].