Comparative analysis of the collisional deactivation of O2(1Δg), O2(1Σ+g), SO(1Σ+), SeO(1Σ+) and NF(1Σ+) by small polyatomic molecules

Abstract

Literature data on the collisional deactivation of the 1Δg and 1Σ+g states of O2 and the 1Σ+ states of SO, SeO and NF are analysed comparatively. Deactivation of the excited diatomic molecule AB from the upper (ABu) to the lower (AB1) electronic state takes place with a rate constant kXY by electronic to vibrational energy transfer to a single terminal bond XY of the quenching molecule. Quenching is considered to occur in coupled transitions ABu(ν=0) → AB1(ν=m) and XY(ν′=0→ν′=n). The variation of kXY over 11 orders of magnitude is reproduced using Franck—Condon factors and energies of the respective transitions. The quantitative evaluation demonstrates that the electronic factors of the ABu→AB1 transitions in the deactivation of the 1Σ+ states of O2, SO, SeO and NF are near unity. This result is in accordance with the observation that the spin-allowed 1Σ+ → 1Δ transition is involved in 1Σ+ deactivation and indicates that symmetry and orbital restrictions disappear in collisional deactivation. The electronic factor of the spin-forbidden 1Δg→3Σ−g quenching of O2 is about 6×10−5 times smaller than that of the spin-allowed 1Σ+g → 1Δg deactivation.