Collisional Relaxation of O(2)(X(3) Sigma(-)(G), Nu=1) and O(2)(A(1) Delta(G), Nu=1) By Atmospherically Relevant Species

Abstract

Laboratory measurements are reported of the rate coefficient for collisional removal of O₂(𝑋³𝛴−_𝑔 , υ = 1) by O(³P), and the rate coefficients for removal of O₂(a¹Δ_g, υ = 1) by O₂, CO₂, and O(³P). A two-laser method is employed, in which the pulsed output of the first laser at 285 nm photolyzesozone to produce oxygen atoms and O₂(a¹Δ_g, υ = 1), and the output of the second laser detects O₂(a¹Δ_g, υ = 1) via resonance-enhanced multiphoton ionization. The kinetics of O₂(𝑋³𝛴−_𝑔 , υ = 1) + O(³P) relaxation is inferred from the temporal evolution of O₂(a¹Δ_g, υ = 1), an approach enabled by the rapid collision-induced equilibration of the O₂(𝑋³𝛴−_𝑔, υ = 1) and O₂(a¹Δ_g, υ = 1) populations in the system. The measured O₂(𝑋³𝛴−_𝑔, υ = 1) + O(³P) rate coefficient is (2.9 ± 0.6) × 10⁻¹² cm³ s⁻¹ at 295 K and (3.4 ± 0.6) × 10⁻¹² cm³ s⁻¹ at 240 K. These values are consistent with the previously reported result of (3.2 ± 1.0) × 10⁻¹² cm³ s⁻¹, which was obtained at 315 K using a different experimental approach [K. S. Kalogerakis, R. A. Copeland, and T. G. Slanger, J. Chem. Phys. 123, 194303 (2005)]. For removal of O₂(a¹Δ_g, υ = 1) by O(³P), the upper limits for the rate coefficient are 4 × 10⁻¹³ cm³ s⁻¹ at 295 K and 6 × 10⁻¹³ cm³ s⁻¹ at 240 K. The rate coefficient for removal of O₂(a¹Δ_g, υ = 1) by O₂ is (5.6 ± 0.6) × 10⁻¹¹ cm³ s⁻¹ at 295 K and (5.9 ± 0.5) × 10⁻¹¹ cm³ s⁻¹ at 240 K. The O₂(a¹Δ_g, υ = 1) + CO₂ rate coefficient is (1.5 ± 0.2) × 10⁻¹⁴ cm³ s⁻¹ at 295 K and (1.2 ± 0.1) × 10⁻¹⁴ cm³ s⁻¹ at 240 K. The implications of the measured rate coefficients for modeling of atmospheric emissions are discussed.