Reactions of Br+at room temperature: state-dependent reactivity of Br+with O2from 0.04 to 5 eV collision energy

Abstract

The reactions of Br+ with a number of gases have been studied at room temperature using a selected-ion flow tube. The presence of at least two states of the Br+ ion was clearly demonstrated in the reaction of Br+ with O2 where one of the Br+ states did not react with a measurable rate coefficient. This unreactive state is presumably the lower fine-structure level of the ground Br+(3Pj) state for which charge transfer with O2 is endothermic by 0.22 eV. This conclusion is supported by the observed onset of reaction of this state at about 0.2 eV collision energy. In each of the other reactions of Br+ studied the two components of Br+ displayed no difference in reactivity and with the exception of reaction with NO the rate coefficients observed approached the classical collision rate kc. The reaction of Br+(3P2) with NO was found to proceed with a rate coefficient of k=4.1*10-11 cm3 s-1 but it was shown that the excited component was quenched with a rate coefficient (kq) close to the collision rate. The energy dependences of the reactions of the two states of Br+ with O2 were studied from room temperature up to a collision energy of 5 eV using a flow-drift tube. At the higher collision energies the rate coefficient observed for the excited component of Br+ was found to be several times higher than the room-temperature classical collision rate. The excited component of Br+ is believed to be a composite of the Br+(3P1) and Br+(3P0) states.