High-Pressure Ion–Molecule Reactions in Carbon Monoxide and Carbon Monoxide–Methane Mixtures

In carbon monoxide at pressures above 0.2 torr, the principal product ion is C2O2+ formed by a three-body process. The rate constant for the reaction is 1.43 × 10−28 cm6 molecule−2·sec−1. Above about 0.8 torr, the reaction appears to approach equilibrium with an equilibrium constant of 1482 referred to 1 atm as standard. At pressures of methane above 0.2 torr and small additions of CO, the only reaction observed in the protonation of CO by CH5+ with a rate constant of 5.54 × 10−10 cm3 molecule−1·sec−1. All other reactions are endothermic and are not observed. At pressures of carbon monoxide above 0.2 torr, the addition of small amounts of methane results in an H-atom transfer reaction to CO+ with a rate constant of 13.7 × 10−10 cm3 molecule−1·sec−1. In addition, C2O2+ reacts to form HCO+, C2H3O+, and C3H3O+ with rate constants of 9.44, 4.37, and 0.76 × 10−10 cm3 molecule−1·sec−1, respectively.