Kinetic Studies of the Reactions of O₂(bΣ_g⁺) with Several Atmospheric Molecules

Abstract

Thermal rate coefficients for the removal (reaction + quenching) of O2(1sigma(g)+) by collision with several atmospheric molecules were determined to be as follows: O3, k3(210-370 K) = (3.63 +/- 0.86) x 10(-11) exp((-115 +/- 66)/T); H2O, k4(250-370 K) = (4.52 +/- 2.14) x 10(-12) exp((89 +/- 210)/T); N2, k5(210-370 K) = (2.03 +/- 0.30) x 10(-15) exp((37 +/- 40)/T); CO2, k6(298 K) = (3.39 +/- 0.36) x 10(-13); CH4, k7(298 K) = (1.08 +/- 0.11) x 10(-13); CO, k8(298 K) = (3.74 +/- 0.87) x 10(-15); all units in cm3 molecule(-1) s(-1). O2(1sigma(g)+) was produced by directly exciting ground-state O2(3sigma(g)-) with a 762 nm pulsed dye laser. The reaction of O2(1sigma(g)+) with O3 was used to produce O(3P), and temporal profiles of O(3P) were measured using VUV atomic resonance fluorescence in the presence of the reactant to determine the rate coefficients for removal of O2(1sigma(g)+). Our results are compared with previous values, where available, and the overall trend in the O2(1sigma(g)+) removal rate coefficients and the atmospheric implications of these rate coefficients are discussed. Additionally, an upper limit for the branching ratio of O2(1sigma(g)+) + CO to give O(3P) + CO2 was determined to be < or = 0.2% and this reaction channel is shown to be of negligible importance in the atmosphere.

O2(b1Σg+) Quenching by O2, CO2, H2O, and N2 at Temperatures of 300–800 K

“…Up to 600 K, the rate constant did not show a significant dependence on temperature. This was in accordance with previous results. , However, between 600 and 800 K, the rate constant increased slightly with temperature. Linear fit of data for 800 K presented in Figure (upper line) gave a value of the rate constant of 5.8 × 10 –13 cm 3 /s.…”

“…Measurements of the rate constants of elementary processes involving O 2 (b 1 Σ g + ) molecules were undertaken by many investigators. For room-temperature conditions, the rate constants for quenching of O 2 (b 1 Σ g + ) were measured repeatedly, for example, by water vapor, ,− carbon dioxide, ,,− nitrogen, ,,, and oxygen. ,− …”

“…Oxygen in the electronically excited state b 1 Σ g + is involved in various chemical, radiative, and energy-exchange processes in the atmosphere, oxygen-containing gas discharges, combustion, and the active medium of an oxygen–iodine laser (OIL) . Reactions with O 2 (b 1 Σ g + ) can produce chemically active atmospheric species such as odd-hydrogen (HO x ) or odd-nitrogen (NO x ) intermediates. , Airglow emission from the O 2 b 1 Σ g + –X 3 Σ g – transition (762 nm) contributes significantly to the radiation budget of the atmosphere . This emission is used to derive atmospheric ozone densities .…”

On the role of excited species in hydrogen combustion

“…However, the O 2 (b¹ g+)-state is very short lived and due to physical quenching relaxes quickly to the lowest lying excited state, O 2 (a¹ g). Collisional deactivation prevails at temperatures relevant to atmospheric chemistry (up to 370 K) [42][43][44] with negligible importance of chemical reactions. Kozlov et al [45] demonstrated that the physical deactivation dominates in the collision of O 2 (a¹ g) and O 2 (b¹ g+) with H 2 up to temperatures of 780-790 K. One may conclude that in the modeling of any technological combustion concept with upstream generation of O 2 (b¹ g+)-state, such as premixed flames, it can be represented by O 2 (a¹ g)-state.…”

O2(b1Σg+) Removal by H2, CO, N2O, CH4, and C2H4 in the 300–800 K Temperature Range

“…Studies of O 2 (b 1 Σ g + ) deactivation at room temperature by molecules relevant to combustion including H 2 , − CH 4 , ,,,,, CO, ,, N 2 O, ,,− and C 2 H 4 , have been reported in many works, a partial list of which is given in Table . The gas temperature in many oxygen-containing mixtures can be much higher than ambient when reactions are in progress, which makes it important to study the kinetics of processes with the O 2 (b 1 Σ g + ) molecule at elevated temperatures.…”