Temperature dependence of the rate constants for the quenching by nitric oxide of the two excited singlet states of molecular oxygen: O2(a1Δg) and O2(b1∑+g)

Abstract
The rate constants for the quenching of both O2(a1Δg) and O2(b1∑+ g) by NO have been measured at 295 K and between 600 and 1100 K by studying the emissions at 634 and 762 nm in the discharge—flow/shock-tube apparatus. At 295 K the rate constants for quenching by NO are (2.10 ± 0.28)× 104 dm3 mol–1 s–1 for O2(a1Δg) and (1.70 ± 0.13)× 107 dm3 mol–1 s–1 for O2(b1∑+ g), which are similar to the values determined previously. The rate constant for quenching of O2(a1Δg) increases with temperature and can be fitted between 295 and 1100 K to a simple Arrhenius equation: kNO d/dm3 mol–1 s–1=(1.90 ± 0.6)× 107 exp [–(2030 ± 50)/T]. For the quenching of O2(b1∑+ g) by NO, the rate constant is nearly independent of temperature but falls slightly above 1000 K. There is, however, a small additional concentration dependence of the rate constant which is presently unexplained. An additional emission is found at high temperatures in mixtures of O2 and NO and it is attributed to chemiluminescence from the reaction between NO and atomic oxygen.

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