Isotope Effects in Methoxy Radical Chemistry

甲氧基自由基化学中的同位素效应

• 批准号: 0937626
• 负责人: Theodore Dibble
• 金额: $ 46.89万
• 依托单位: SUNY College of Environmental Science and Forestry
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0937626&HistoricalAwards=false
• 关键词: Isotope; Effects; Methoxy; Radical; Chemistry

This project has three goals: 1) Experimentally determine the branching ratio for abstraction of hydrogen atoms (H) versus deuterium atoms (D) from mono-deuterated methoxy radicals (CH2DO*) in their reaction with molecular oxygen (O2) as a function of temperature; 2) Experimentally determine absolute rate constants for CH3O* and CD3O* reacting with O2 as a function of temperature; 3) Compute rate constants for methoxy + O2 reactions, including tunneling and variational effects, and extend calculations to larger radicals. Two experimental approaches will be used: Fourier Transform Infrared (FTIR) spectroscopy in the reaction chamber of collaborators at the National Center for Atmospheric Research (NCAR) will be used to determine the branching ratio for production of deuterated versus normal formaladhyde in the CH2DO* + O2 reaction. Rate constant ratios for reaction of CH3O* and CD3O* radical with O2 (kO2) and NO2 (kNO2) will also be determined at NCAR from product yields. Experiments at NCAR will be carried out by one of the Principal Investigator's (PI) graduate students under the direct supervision of senior scientists at NCAR. Direct measurements of kNO2 at the PI's lab (SUNY-ESF) will be carried out using laser flash photolysis to generate radicals and laser-induced fluorescence for time-resolved detection. The combination of kNO2/kO2 from NCAR with kNO2 from SUNY-ESF will enable determination of kO2(T) for both CH3O* and CD3O*. Direct measurements of kO2 at SUNY-ESF will validate the combined results. An understanding of the isotope effects in these reactions will be achieved via high-level quantum calculations coupled to cutting-edge algorithms for statistical rate theory and multi-dimensional tunneling calculations. Calculations will be extended to larger alkoxy radicals. This research will be the first to determine kO2 at temperatures less than 298 K for methoxy radical. It will also be the first temperature-dependent determination of branching ratio for production of normal and deuterated formaldehyde in the CH2DO* + O2 reaction, and only the second study of this branching ratio. The calculations will provide benchmarks for reliable calculations of kO2(T) for a diverse range of alkoxy radicals of tropospheric interest.By enhancing other researchers' abilities to calculate reliable values of kO2(T), this research will lead to a much better understanding, not just of alkoxy radical chemistry, but also of the overall mechanisms of degradation of many classes of volatile organic compounds (VOCs). This will help improve representations of VOC degradation processes in models of air pollution and global tropospheric chemistry, contributing to more effective ozone abatement plans and better modeling of climate-chemistry feedbacks. The results will also constrain the mechanism of deuterium enrichment of molecular hydrogen in the atmosphere, and improve our understanding of the atmospheric budget of molecular hydrogen. This will help to understand the potential impacts of a hydrogen economy on microbial communities, stratospheric and local ozone, and the abundance of greenhouse gases. Two graduate students and several undergraduates working on this project will grow intellectually and professionally, and gain advanced technical knowledge of diverse experimental and computational methods for kinetics.

该项目有三个目标：1）实验测定从单氘代甲氧基（CH 2DO *）与分子氧（O 2）反应中提取氢原子（H）与氘原子（D）的分支比作为温度的函数; 2）实验测定CH 3 O * 和CD 3 O * 与O 2反应的绝对速率常数作为温度的函数; 3）计算甲氧基+ O2反应的速率常数，包括隧道效应和变分效应，并将计算扩展到更大的自由基。将使用两种实验方法：在国家大气研究中心（NCAR）的合作者的反应室中的傅里叶变换红外光谱（FTIR）将用于确定在CH 2DO * + O2反应中产生氘代甲醛与正常甲醛的分支比。CH 3 O * 和CD 3 O * 自由基与O2（kO 2）和NO2（kNO 2）反应的速率常数比也将在NCAR根据产物产率确定。NCAR的实验将由主要研究者（PI）的一名研究生在NCAR高级科学家的直接监督下进行。将在PI实验室（SUNY-ESF）使用激光闪光光解产生自由基和激光诱导荧光进行时间分辨检测，从而直接测量KNO 2。NCAR的kNO 2/kO 2与SUNY-ESF的kNO 2相结合，将能够确定CH 3 O * 和CD 3 O * 的kO 2（T）。SUNY-ESF对kO 2的直接测量将验证综合结果。在这些反应中的同位素效应的理解将通过高层次的量子计算耦合到尖端算法的统计速率理论和多维隧道计算实现。计算将扩展到更大的烷氧基。这项研究将是第一个确定kO 2的温度低于298 K的甲氧基自由基。这也将是第一个温度依赖的分支比的测定生产正常和氘代甲醛在CH 2DO * + O2反应，只有第二次研究这种分支比。通过提高其他研究人员计算kO 2（T）可靠值的能力，这项研究将导致更好的理解，不仅是烷氧基自由基化学，而且是许多类别的挥发性有机化合物（VOCs）的降解的整体机制。这将有助于改善空气污染和全球对流层化学模型中挥发性有机化合物降解过程的表现，有助于更有效的臭氧减排计划和更好的气候化学反馈建模。这一结果也将有助于解释氢分子在大气中氘富集的机理，并有助于加深我们对氢分子大气收支的理解。这将有助于了解氢经济对微生物群落、平流层和当地臭氧以及温室气体丰度的潜在影响。两名研究生和几名本科生在这个项目上工作将增长智力和专业，并获得不同的实验和计算方法的动力学先进的技术知识。