Collisional quenching of singlet molecular oxygen, O2(a1Δg) and O2(b1Σ +g), by ammonia at high temperatures

Abstract

The discharge-flow/shock-tube technique has been used to measure the temperature dependence of the collisional quenching of singlet molecular oxygen, O₂(b¹Σ⁺_g) and O₂(a¹Δ_g), by NH₃ between 600 and 1150 K.

For the quenching of O₂(b¹Σ⁺_g) by NH₃, the rate constant at 295 K is (7.50 ± 0.10)× 10⁸ dm³ mol^–1 s^–1. The rate constant is found to be independent of temperature between 210 and ca. 750 K; above 750 K the value falls slowly to 2.5 × 10⁸ dm³ mol^–1 s^–1 at 1150 K. Thus NH₃ fits the pattern of efficient quenchers of O₂(b¹Σ⁺_g). In this work the analysis method has been modified to allow for efficient quenchers and the new approach has allowed us to verify the analysis used previously.

The rate constant for the quenching of O₂(a¹Δ_g) by NH₃ was too slow at high temperatures to measure within the timescale of our experiment. The value at 295 K is (5.37 ± 0.14)× 10³ dm³ mol^–1 s^–1 and the upper limit at 1150 K is 1.3 × 10⁴ dm³ mol^–1 s^–1.