Activation of dioxygen by halocarbon ions

Tandem mass spectrometry is used to show that low energy collisions of ioni zed halocarbenes, including CBr2.+ and CBrCl.+, with molecular oxygen lead to (i) decarbonation with formation of the dihalogen molecular cation and ( ii) oxygenolysis yielding BrCO+. Both reactions may occur via the same ion- molecule addition product of molecular oxygen and the ionized carbene. Reac tion is favored at low collision energies, such as are encountered in an io n trap. insights into the energetics of the reactions of CBr2.+ with O-2 ar e obtained from ab initio molecular orbital theory. Other aspects of the po sitive ion chemistry of dioxygen with various halogen-containing ions are a lso discussed. Dioxygen activation by halocarbon ions suggests additional c hannels that might affect the fate of halocarbons and the ozone balance in the atmosphere.