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(a¹Δ_g) 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(a¹Δ_g) 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(a¹Δ_g) increases with temperature and can be fitted between 295 and 1100 K to a simple Arrhenius equation: k^NO_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.