Atmospheric Chemistry Special Feature: Reactive and nonreactive quenching of O(1D) by the potent greenhouse gases SO2F2 NF3 and SF5CF3

摘要

A laser flash photolysis–resonance fluorescence technique has been employed to measure rate coefficients and physical vs. reactive quenching branching ratios for O(¹D) deactivation by three potent greenhouse gases, SO2F2(k1), NF3(k2), and SF5CF3(k3). In excellent agreement with one published study, we find that k1(T) = 9.0 × 10^-11 exp(+98/T) cm³ molecule^-1 s^-1 and that the reactive quenching rate coefficient is k1b = (5.8 ± 2.3) × 10^-11 cm³ molecule^-1 s^-1 independent of temperature. We find that k2(T) = 2.0 × 10^-11 exp(+52/T) cm³ molecule^-1 s^-1 with reaction proceeding almost entirely (∼99%) by reactive quenching. Reactive quenching of O(¹D) by NF3 is more than a factor of two faster than reported in one published study, a result that will significantly lower the model-derived atmospheric lifetime and global warming potential of NF3. Deactivation of O(¹D) by SF5CF3 is slow enough (k3 < 2.0 × 10^-13 cm³ molecule^-1 s^-1 at 298 K) that reaction with O(¹D) is unimportant as an atmospheric removal mechanism for SF₅CF₃. The kinetics of O(¹D) reactions with SO₂ (k₄) and CS₂ (k₅) have also been investigated at 298 K. We find that k₄ = (2.2 ± 0.3) × 10^-10 and k₅ = (4.6 ± 0.6) × 10^-10 cm³ molecule^-1 s^-1; branching ratios for reactive quenching are 0.76 ± 0.12 and 0.94 ± 0.06 for the SO₂ and CS₂ reactions, respectively. All uncertainties reported above are estimates of accuracy (2σ) and rate coefficients k_i(T) (i = 1,2) calculated from the above Arrhenius expressions have estimated accuracies of ± 15% (2σ).