Isotope Effects in Methoxy Radical Chemistry

这个项目有三个目标：1)实验确定从单氚甲氧基自由基(CH2DO*)与分子氧(O2)反应中提取氢原子(H)与氢原子(D)的分支比(D)作为温度的函数；2)实验确定CH3O*和CD3O*与O2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：国家大气研究中心(NCAR)合作者反应室中的傅里叶变换红外(FTIR)光谱将用于确定CH2DO*+O2反应中生产重氢与正常甲醛的分支比。CH3O*和Cd3O*与O2(KO2)和NO2(KNO2)反应的速率常数比也将在NCAR根据产物产率确定。NCAR的实验将由首席研究员(PI)的一名研究生在NCAR资深科学家的直接监督下进行。将在PI的实验室(SUNY-ESF)直接测量KNO2，使用激光闪光光解产生自由基，并使用激光诱导荧光进行时间分辨检测。将来自NCAR的KNO2/KO2与来自SUNY-ESF的KNO2相结合，可以同时测定CH3O*和CD3O*的KO2(T)。在纽约州立大学ESF对KO2的直接测量将验证综合结果。对这些反应中的同位素效应的理解将通过高级量子计算与用于统计速率理论和多维隧道计算的尖端算法相结合来实现。计算将扩展到更大的烷氧基。这项研究将首次在低于298K的温度下测定甲氧基的KO2。这也将是第一次对CH2DO*+O2反应中产生的正常和重氢甲醛的支化比进行随温度变化的测定，也是对该支化比的第二次研究。这些计算将为各种对流层感兴趣的烷氧基的可靠计算提供基准。通过提高其他研究人员计算可靠的KO2(T)值的能力，这项研究将使我们不仅更好地理解烷氧基化学，而且还将更好地理解许多类挥发性有机化合物(VOCs)的整体降解机理。这将有助于改进在空气污染和全球对流层化学模式中对VOC降解过程的描述，有助于更有效地制定臭氧削减计划和更好地模拟气候化学反馈。这一结果还将约束分子氢在大气中的富氢机理，并提高我们对大气中分子氢收支的理解。这将有助于理解氢经济对微生物群落、平流层和局地臭氧以及温室气体丰度的潜在影响。在这个项目中工作的两名研究生和几名本科生将在智力和专业上成长，并获得各种动力学实验和计算方法的高级技术知识。

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.