Laboratory Formation of OBrO and Its Reactivity toward Ozone at 298 K

Bromine dioxide, OBrO, has been formed in our laboratory using three methods in a discharge flow reactor: (1) O + Br 2; (2) Br + O 3; and (3) microwave discharge of a Br 2 /O 2 /He mixture. The OBrO radical was detected using a mass spectrometer at m / e = 111/113. A new mechanism is proposed to account for the formation of the OBrO in these methods. The key to this mechanism is the self-reaction of vibrationally excited BrO. At 298 K, ground-state OBrO does not notably react with ozone, and an upper limit rate constant for the reaction of the ground-state OBrO with ozone was estimated to be k 13 ≤ 5 × 10 -16 cm 3 molecule -1 s -1 . The vibrationally excited OBrO, on the other hand, is at least 3 orders of magnitude more reactive toward ozone than the ground-state OBrO, with a rate constant of k 13a = (5.4 ± 2.7) × 10 -13 cm 3 molecule -1 s -1 .