Oxygen negative ion reactions with carbon dioxide and carbon monoxide. Part 2

The rate constant of the clustering reaction O–2+ 2CO2→ CO–4+ CO2 has been measured for near-thermal ions in a drift tube and mass filter and found to be 1.2 ± 0.2 × 10–28 ml2 molecule–2 s–1 at 298 K and pressures in the region of 1 Torr. The similar reaction with CO, O–2+ CO + CO2→ CO–3+ CO2, has been shown to have a rate constant more than 100 times smaller. An upper limit of 10–16 ml molecule–1 s–1 is found for the reaction CO–4+ CO → CO–3+ CO2. It is concluded that the values of these rate constants, together with those measured earlier 1 for O– cluster reactions, do not allow sufficient reoxidation of CO to CO2 by simple ground-state oxygen negative ions to explain the apparent radiation stability of CO2. Some alternative mechanisms are considered.