Abstract
The quenching of N2(A 3Σ+u) metastables by Br2(X 1Σ+g) results in the generation of Br2(D′ 3Π2g)→A′(3Π2u) emission. Although this energy exchange is near resonant, its rate constant is only (5±2)×10−13 cm3 molecule−1 s−1. Comparison of this result with the known rate for N2(A 3Σ+u) quenching by I2 indicates the importance of Franck–Condon factors in these energy transfer processes. In light of this result, the generation of intense Br2 D′→A′ emission from the UV photolysis of BrN3 is modeled as a Franck–Condon favored process in which Br2(A′ 3Π2u or A 3Π1u) is excited to the D′(3Π2g) state by collisions with N2(A 3Σ+u) metastables. Br2 (A or A′) is generated as a product of the reaction of bromine atoms, produced as a photodissociation fragment, with BrN3. The rate constant for this process is k5=(3.0±0.5)×10−11 cm3 molecule−1 s−1. The rate constant of the energy transfer process is inferred to be k6≥1.5×10−10 cm3 molecule−1 s−1. A second mechanism producing Br2(D′ 3Π2g) is evident in the time profile of the D′→A′ emission. This mechanism, which produces prompt D′→A′ emission, does not involve excitation by collisions with N2(A).
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