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Excited molecules in gaseous flow sytems : kinetics and mechanisms of the Formation and reactions of O2 (1Ag) and O2 (1Eg).

University of British Columbia

When oxygen is passed through a microwave discharges, the oxygen atoms being destroyed by distilling mercury through the discharges an excited molecule O₂(¹△g) was observed to be the primary discharge product. This excited molecule was found to be immune to collisional deactivation by a wide range of added foreign gasses, with the exception of certain substituted ethylenes which it oxidized. The principal mode of decay of O₂(¹△g) was nonradiative decay, with knonrad. equal to 0,178 sec.-¹ The excited molecule O₂(¹△g) however, was observed to undergo two novel energy pooling processes, [ Formulas omitted ] The first of these energy pooling processes gave rise to two broad structureless bands at 6340 A and 7030 A which had not previously been observed in discharged oxygen. These bands, the intensity of which is proportional to the square of the O₂(¹△g) concentration and independent of the total pressure in the systems are believed to result from a simultaneous electronic transition in two O₂(¹△g) molecules with the emission of a single photon. The 6340 A band appears if both molecules undergo a (0-0) transition in the [ Formula omitted ] system and the 7030 A. band if one molecule undergoes a (0-0) transition and the other a (0-1) transition. The second of these energy pooling processes is a disproportionation reaction which leads to the formation of a second excited molecule [ Formula omitted ]. Tne rate constant, for this reaction was found to be 1.3 x 10³ l.moles -¹sec.-¹, in disagreement with the results of Young and Black by a factor of 10⁴ Both energy pooling processes are believed to have a common intermediate, { O₂(¹△g) }2, which is either a metastable double molecule or a colliding pair of molecules. The principal mode of decay of [ Formula omitted ]was nonradiative decay, with knonrad. equal to 64.6 sec.-¹ Unlike O₂(¹△g) , [ Formula omitted ] was found to be collisionally deactivated by a wide variety of added foreign gases, with the most effective deactivator tried being water. The rate constants for the reaction [ Formula omitted ] were determined for fourteen different quenchers. A good correlation between quenching efficiency and the magnitude of the intermolecular potential between the quencher and [ Formula omitted ] has been obtained. Two additional energy pooling processes involving excited oxygen molecules and either molecular iodine or nitrogen dioxide were observed. Both resulted in the formation of an excited molecule[ Formula omitted ]or NO₂, which emitted in the visible.

Text

2011-08-10

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http://hdl.handle.net/2429/36634

Chemistry

University of British Columbia

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