The low-temperature quenching of singlet molecular oxygen [O2(a1Δg)]

Abstract

An apparatus has been constructed to study the quenching and emission reactions of O₂(a¹Δ_g) at temperatures between 100 and 450 K and measurements have been made of the quenching of O₂(a¹Δ_g) by oxygen itself in this range. The rate constant was found to be k/dm³ mol^–1 s^–1=(1896 ± 65) exp [–(205 ± 8)/T]. The results agree well with those recently obtained at high pressures with laser excitation of O₂(a¹Δ_g) and also, within the range, fit with the predictions of a theory in which the electronic energy is distributed as vibrational energy between the two quenchers. However, the detailed temperature dependence is not predicted correctly and this is attributed to the neglect of the possible temperature dependence of the curve-crossing between O₂(a¹Δ_g) and O₂(X³Σ^–_g). A comparison is made between the observed temperature dependences of the quenching reactions of O₂(a¹Δ_g) and O₂(b¹Σ⁺_g).