Parahydrogen Matrix Isolation Infrared Spectroscopy and Kinetics

在化学系化学结构、动力学和机理(CSDM-A)计划的支持下，怀俄明大学的David T.Anderson教授和他的团队正在使用由分子氢制成的极冷晶体作为反应容器，以研究低温化学。该研究项目的第一个重点是研究氢原子的扩散和反应性。在极低的温度(-457华氏度)下，氢原子更好地被描述为物质波，而不是粒子，这对它们如何在晶体中扩散并与其他物种发生化学反应有重大影响。在这些低温条件下，化学被转化为完全量子力学的状态，在那里可以发现意想不到的化学行为。这项工作的第二个重点是对经历快速冷却、光化学反应或化学反应的多原子分子中的核自旋态进行实验研究。核自旋是指原子的内部状态，有时是有取向的。某些分子，比如水，有两种不同的形式，一种是两个氢原子的核自旋方向一致，另一种是两个氢原子的自旋方向相反。这些不同的水的核自旋异构体具有不同的磁性。安德森教授领导的研究小组正在研究核自旋在各种物理和化学过程中的保守程度，目的是学习如何利用核自旋来控制化学反应，并增强磁成像技术。这项实验工作使用定制设计的低温装置，在1.5至5K的温度范围内合成掺有百万分之几化学杂质的对氢(分子氢的一种特定的核自旋异构体)晶体。利用各种紫外光光源原位生成氢原子，并使用高分辨率傅里叶变换红外光谱测量随后的反应动力学。安德森教授和他的团队利用液氦低温恒温器来实现如此低的温度，并建造了一个专门的氦回收系统来回收废氦气体，以最大限度地减少供应成本。与安德森教授合作的学生获得了使用实验物理化学中复杂方法的经验，这些方法探索量子材料的物理化学性质，这些材料的性质受量子力学定律的支配。学生参与这项研究对未来科学家进行低温化学技术和物质量子力学操作方面的培训具有重大影响。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor David T. Anderson and his group at the University of Wyoming are using extremely cold crystals made from molecular hydrogen as a reaction vessel to investigate chemistry at low temperatures. The first thrust of the research project examines the diffusion and reactivity of hydrogen atoms. At extremely low temperatures (-457°F), hydrogen atoms are better described as matter waves instead of particles, which has a major impact on how they diffuse through the crystal and react chemically with other species. Chemistry is transformed under these low-temperature conditions into the fully quantum mechanical regime where unexpected chemical behavior can be discovered. The second thrust of the work involves experimental studies of nuclear spin states in polyatomic molecules that undergo rapid cooling, photochemistry, or chemical reactions. Nuclear spin refers to the internal state of an atom, and sometimes has an orientation. Certain molecules, like water, come in two different forms, one where the two hydrogen atoms have their nuclear spins aligned in the same direction, and the other with the two hydrogen atom spins aligned in opposite directions. These different nuclear spin isomers of water have different magnetic properties. The research team led by Professor Anderson is examining to what extent nuclear spin is conserved during various physical and chemical processes, with the goal of learning how to use nuclear spin to control chemical reactions and to enhance magnetic imaging techniques. This experimental work uses a custom-designed cryogenic apparatus to synthesize cryocrystals of para-hydrogen (a specific nuclear spin isomer of molecular hydrogen) doped with parts per million concentrations of chemical impurities at temperatures in the 1.5 to 5 K range. Hydrogen atoms are created in situ using a variety of ultraviolet light sources and the ensuing reaction kinetics are measured using high-resolution Fourier-transform infrared spectroscopy. Professor Anderson and his group utilize a liquid helium cryostat to achieve such low temperatures and have built a dedicated helium recovery system to recycle the spent helium gas to minimize supply costs. The students working with Professor Anderson gain experience using sophisticated methods in experimental physical chemistry that probe the physical and chemical properties of quantum materials, materials whose properties are dominated by the laws of quantum mechanics. The involvement of students in the research has a significant impact by training future scientists in the techniques of low-temperature chemistry and the quantum-mechanical manipulation of matter.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.