Parahydrogen Matrix Isolation Infrared Spectroscopy and Kinetics

在化学系化学结构、动力学和机理-A（CSDM-A）项目的支持下，大卫T.怀俄明州大学的安德森和他的小组正在使用由分子氢制成的极冷晶体作为反应容器来研究低温下的化学。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 ° F）下，氢原子更好地描述为物质波而不是粒子，这对它们如何通过晶体扩散并与其他物质发生化学反应产生了重大影响。 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，有时具有取向。 某些分子，如水，有两种不同的形式，一种是两个氢原子的核自旋方向相同，另一种是两个氢原子的核自旋方向相反。 水的这些不同的核自旋异构体具有不同的磁性。 由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控制化学反应和增强磁成像技术。 这项实验工作使用定制设计的低温装置，在1.5至5 K的温度范围内合成掺杂有百万分之一浓度的化学杂质的仲氢（分子氢的特定核自旋异构体）的低温晶体。 氢原子是使用各种紫外光源原位产生的，随后的反应动力学是使用高分辨率傅里叶变换红外光谱法测量的。 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，并建立了一个专用的氦气回收系统来回收用过的氦气，以最大限度地降低供应成本。 与安德森教授一起工作的学生使用实验物理化学中的复杂方法获得经验，这些方法可以探测量子材料的物理和化学性质，这些材料的性质受量子力学定律的支配。通过培养未来的科学家掌握低温化学和物质的量子力学操纵技术，学生参与研究产生了重大影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值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.