Competing Pathways in Reactions of Oxygen-Containing Free Radicals

通过这个奖项，由化学结构，动力学和机制-化学系的计划资助，H。弗洛伊德戴维斯和康奈尔大学的学生将研究涉及大气中重要的含氧自由基的光诱导和双分子反应。 使用交叉激光分子束方法，将确定竞争的二氧化溴和二氧化碘光解途径的分支比。 涉及双原子卤素氧化物自由基的基本自由基-自由基反应（例如，ClO + BrO）将在交叉分子束中进行研究。 将开发一种涉及光耗尽的高活性中性卤素氧化物分子与近阈值光电离检测的方法，以确定波长依赖的吸收截面的物种，不能在纯的形式制备。 拟议的研究将提供实验基准，包括电离能、键离解能和由太阳辐射吸收或双分子碰撞引起的关键大气反应的分支比。 这些数量应有助于直接测试反应的量子理论模型，并应用于臭氧消耗过程的大气模型。卤素原子（氯、溴和碘）在地球大气中发生反应，破坏臭氧，臭氧是一种重要的分子，可以保护人们免受有害的紫外线太阳辐射。 破坏臭氧层的反应涉及带有未成对电子的分子，即所谓的自由基。 由于它们具有极强的反应性，大多数自由基不能以纯的形式制备，这使得它们的研究变得困难。 在该研究项目中，使用激光束（准直光束）和分子束（准直分子束）等实验室技术来研究涉及大气自由基的化学反应。 此外，戴维斯小组将建立一个高中贷款计划，为新开发的低成本（25美元）吸收光谱仪。这将有助于把动手实验室实验，通常需要高成本的设备，高中教室。让高中生接触科学仪器的设计、建造和使用，可以用来教授批判性思维技能，帮助学生理解和欣赏科学。

Through this award, funded by the Chemical Structure, Dynamics, and Mechanisms - A Program of the Division of Chemistry, Prof. H. Floyd Davis and students at Cornell University will study photoinduced and bimolecular reactions involving atmospherically important oxygen-containing free radicals. Using the crossed laser- molecular beam method, the branching ratios for competing bromine dioxide and iodine dioxide photodissociation pathways will be determined. Elementary radical-radical reactions involving diatomic halogen oxide free radicals (e.g., ClO + BrO) will be studied in crossed molecular beams. A method involving photodepletion of highly-reactive neutral halogen oxide molecules with near-threshold photoionization detection will be developed to determine wavelength-dependent absorption cross sections for species that cannot be prepared in pure form. The proposed studies will provide experimental benchmarks, including ionization energies, bond dissociation energies, and branching ratios for key atmospheric reactions induced by absorption of solar radiation or bimolecular collisions. These quantities should help facilitate direct tests of quantum theoretical models for reactions, and should be of use in atmospheric models for ozone-depleting processes. Halogen atoms (chlorine, bromine, and iodine) undergo reactions in the Earth's atmosphere that destroy ozone, an important molecule that provides protection from harmful ultraviolet solar radiation. The ozone-destroying reactions involve molecules with unpaired electrons known as free radicals. Because of their extremely reactive nature, most free radicals cannot be prepared in pure form, making their study difficult. In this research project, laboratory techniques involving laser beams (collimated beams of light) and molecular beams (collimated beams of molecules), are used to study chemical reactions involving atmospheric free radicals. In addition, the Davis group will establish a high-school lending program for newly-developed low-cost ($25) absorption spectrometers. This will help bring hands-on laboratory experiments, usually requiring high-cost equipment, to the high school classroom. Exposing high school students to the design, construction, and use of scientific instruments can be used to teach critical thinking skills and help students understand and appreciate science.