Kinetic Study of the OH + Glyoxal Reaction: Experimental Evidence and Quantification of Direct OH Recycling

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• 作者：James Lockhart ; Mark Blitz ; Dwayne Heard ; Paul Seakins ; Robin Shannon
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：October 31, 2013
• 年：2013
• 卷：117
• 期：43
• 页码：11027-11037
• 全文大小：461K
• 年卷期：v.117,no.43(October 31, 2013)
• ISSN：1520-5215

文摘

The kinetics of the OH + glyoxal, (HCO)₂, reaction have been studied in N₂ and N₂/O₂ bath gas from 5鈥?0 Torr total pressure and 212鈥?95 K, by monitoring the OH decay via laser induced fluorescence (LIF) in excess (HCO)₂. The following rate coefficients, k_OH+(HCO)2 = (9.7 卤 1.2), (12.2 卤 1.6), and (15.4 卤 2.0) 脳 10p>鈥?2p> cmp>3p> moleculep>鈥?p> sp>鈥?p> (where errors represent a combination of statistical errors at the 2蟽 level and estimates of systematic errors) were measured in nitrogen at temperatures of 295, 250, and 212 K, respectively. Rate coefficient measurements were observed to be independent of total pressure but decreased following the addition of O₂ to the reaction cell, consistent with direct OH recycling. OH yields, 桅_OH, for this reaction were quantified experimentally for the first time as a function of total pressure, temperature, and O₂ concentration. The experimental results have been parametrized using a chemical scheme where a fraction of the HC(O)CO population promptly dissociates to HCO + CO, the remaining HC(O)CO either dissociates thermally or reacts with O₂ to give CO₂, CO, and regenerate OH. A maximum 桅_OH of (0.38 卤 0.02) was observed at 212 K, independent of total pressure, suggesting that 60% of the HC(O)CO population promptly dissociates upon formation. Qualitatively similar behavior is observed at 250 K, with a maximum 桅_OH of (0.31 卤 0.03); at 295 K, the maximum 桅_OH decreased further to (0.29 卤 0.03). From the parametrization, an OH yield of 桅_OH = 0.19 is calculated for 295 K and 1 atm of air. It is shown that the proposed mechanism is consistent with previous chamber studies. While the fits are robust, experimental evidence suggests that the system is influenced by chemical activation and cannot be fully described by thermal rate coefficients. The atmospheric implications of the measurements are briefly discussed.