Alkali Aggregates on Cold Helium Droplets and in Free Jets

冷氦液滴和自由射流中的碱聚集

• 批准号: 9901291
• 负责人: Wolfgang Ernst
• 金额: $ 42.55万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-01 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9901291&HistoricalAwards=false
• 关键词: Alkali; Aggregates; Cold; Helium; Droplets

In this project funded by the Experimental Physical Chemistry program of the Chemistry Division and the Atomic, Molecular, Optical, and Plasma Physics program of the Physics Division, Wolfgang Ernst of Pennsylvania State University will study intramolecular interactions in metallic aggregates, specifically, small alkali-atom clusters. Molecular beam spectroscopy using narrow-band lasers and microwave radiation as well as laser ionization and mass selective detection will be used to investigate species produced using two different methods. In the first technique free-jet expansions of alkali metal vapors will generate small alkali clusters that are studied at very high resolution using resonant two-photon ionization (R2PI) spectroscopy, ionization detected microwave spectroscopy, and optical-optical double resonance. Insight into details of Jahn-Teller (JT) and pseudo Jahn-Teller potential energy surfaces will result, and questions about a Berry phase in the evolution of nuclear and electronic wavefunctions will be answered. In the second set of experiments alkali aggregates will form on cold helium droplets, which act as inert substrates. The metal aggregates acquire the 0.4 K temperature of the droplets, and the resulting simplified spectra will be studied by laser-induced fluorescence, laser-microwave double resonance, laser ionization, and time-of-flight mass spectroscopy. Species investigated will include different alkali metals and products of reactions of alkalis with simple molecules. Spectroscopy of atomic and molecular species on ultracold helium drops is similar to matrix isolation spectroscopy and can give correspondingly useful information about unstable chemical intermediates. Results of this work can also be effective in testing quantum chemical calculations and molecular dynamics models, developing schemes for coherent control of molecules using femtosecond laser pulses, and understanding reactions involving other small gas-phase species, such as air pollutants and reactive intermediates of combustion processes.

在这个由化学系的实验物理化学计划和物理系的原子、分子、光学和等离子体物理计划资助的项目中，宾夕法尼亚州立大学的沃尔夫冈·恩斯特将研究金属聚集体中的分子内相互作用，特别是小的碱原子团簇。使用窄带激光和微波辐射的分子束光谱以及激光电离和质量选择检测将用于研究使用两种不同方法产生的物种。在第一种技术中，碱金属蒸气的自由喷射膨胀将产生小的碱团簇，并使用共振双光子电离(R2PI)光谱、电离探测微波光谱和光学-光学双共振对其进行高分辨率的研究。将深入了解Jahn-Teller(JT)和伪Jahn-Teller势能面的细节，并回答有关核和电子波函数演化中的Berry相的问题。在第二组实验中，作为惰性底物的冷氦液滴上将形成碱聚集体。金属聚集体获得液滴的0.4K温度，得到的简化光谱将用激光诱导荧光、激光-微波双共振、激光电离和飞行时间质谱仪进行研究。研究的种类将包括不同的碱金属和碱与简单分子反应的产物。超冷氦滴上原子和分子物种的光谱类似于基质隔离光谱，可以相应地提供关于不稳定化学中间体的有用信息。这项工作的结果也可以有效地测试量子化学计算和分子动力学模型，开发使用飞秒激光脉冲对分子进行相干控制的方案，以及理解涉及其他小气相物种的反应，如空气污染物和燃烧过程的活性中间体。