Rate coefficients for the reaction of O(¹D) with the atmospherically long-lived greenhouse gases NF₃, SF₅CF₃, CHF₃, C₂F₆, c-C₄F₈, n-C₅F₁₂, and n-C₆F₁₄

Abstract. The contribution of atmospherically persistent (long-lived) greenhouse gases to the radiative forcing of Earth has increased over the past several decades. The impact of highly fluorinated, saturated compounds, in particular perfluorinated compounds, on climate change is a concern because of their long atmospheric lifetimes, which are primarily determined by stratospheric loss processes, as well as their strong absorption in the infrared "window" region. A potentially key stratospheric loss process for these compounds is their gas-phase reaction with electronically excited oxygen atoms, O(¹D). Therefore, accurate reaction rate coefficient data is desired for input to climate change models. In this work, rate coefficients, k, were measured for the reaction of O(¹D) with several key long-lived greenhouse gases, namely NF₃, SF₅CF₃, CHF₃ (HFC-23), C₂F₆, c-C₄F₈, n-C₅F₁₂, and n-C₆F₁₄. Room temperature rate coefficients for the total reaction, k_Tot, corresponding to loss of O(¹D), and reactive channel, k_R, corresponding to the loss of the reactant compound, were measured for NF₃ and SF₅CF₃ using competitive reaction and relative rate methods, respectively. k_R was measured for the CHF₃ reaction and improved upper-limits were determined for the perfluorinated compounds included in this study. For NF₃, k_Tot was determined to be (2.55 ± 0.38) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k_R, which was measured using CF₃Cl, N₂O, CF₂ClCF₂Cl (CFC-114), and CF₃CFCl₂ (CFC-114a) as reference compounds, was determined to be (2.21 ± 0.33) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. For SF₅CF₃, k_Tot = (3.24 ± 0.50) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ and k_R < 5.8 × 10^×14 cm³ molecule⁻¹ s⁻¹ were measured, where k_R is a factor of three lower than the current recommendation of k_Tot for use in atmospheric modeling. For CHF₃ k_R was determined to be (2.35 ± 0.35) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, which corresponds to a reactive channel yield of 0.26 ± 0.04, and resolves a large discrepancy among previously reported values. The quoted uncertainties are 2σ and include estimated systematic errors. Upper-limits for k_R for the C₂F₆, c-C₄F₈, n-C₅F₁₂, and n-C₆F₁₄ reactions were determined to be 3.0, 3.5, 5.0, and 16 (in units of 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹), respectively. The results from this work are compared with results from previous studies. As part of this work, infrared absorption band strengths for NF₃ and SF₅CF₃ were measured and found to be in good agreement with recently reported values.