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UBC Theses and Dissertations

Kinetic studies of O(¹S) formation from atomic oxygen recombination Wassell, Peter Thomas


The molecular and atomic dependencies of the O(¹S) emission have been studied in the laboratory by generating oxygen atoms in a discharge flow system. The intensity of the emission is found to have the dependence [See thesis for equation] where M is the total particle concentration in the system. From absolute measurements of the O(¹S) atomic line, the overall rate constant k[sub T] is found to be equal to 2.7 ± 0.3 x 10⁻²⁷cm⁶s⁻¹ at 300K. The observed dependence is shown to be inconsistent with the proposed Chapman mechanism for the excitation of O(¹S) [See thesis for equation] (1) However the observations are found to be in agreement with a "Barth-type" mechanism, where a metastable oxygen molecule (O₂*) is formed in the recombination of two oxygen atoms in the presence of a third body, [See thesis for equation] (2) followed by energy transfer to a third oxygen atom to form O(¹S) [See thesis for equation] (3) and the radiative emission of O(¹S) at 557.7 nm. The possible electronic states of O₂ corresponding to O₂* are dis-cussed. Although the identity of the O₂* remains to be found, the major loss process of this intermediate is found to be quenching by atomic oxygen in [See thesis for equation] (4) rather than by molecular oxygen or argon [See thesis for equation] quenched products (5) [See thesis for equation] quenched products (6) Until recently the major quencher of O(¹S) was thought to be the ground-state oxygen atom [See thesis for equation] quenched products (7) However, in this system, the dependence of the 557.7 nm emission found to be consistent with the predominate quenching of O(¹S) by O₂(a¹Δg): [See thesis for equation] quenched products (8) The rate constant k₈ is estimated to be 7 ± 3 x 10⁻¹⁰cm³ s⁻¹ by comparison for quenching of O(¹S) by O₂. [See thesis for equation] quenched products (9) O₂(a¹Δg) is expected to be present in all laboratory systems involving atomic oxygen due to its formation by either heterogeneous or homogeneous recombination of O[³P]. Due to the magnitude of k₈, O₂(a¹Δg) is expected to be the major quencher of O(¹S) in most of these systems. Using currently accepted values for the concentration of O₂(a¹Δg) in the terrestrial nightglow layer, the quenching of O(¹S) by O₂(a¹Δg) is found to be unimportant in this region compared to its radiative decay. Other atmospheric implications of this investigation's results are discussed.

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