Parahydrogen Matrix Isolation Infrared Spectroscopy and Kinetics

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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.