******NON-TECHNICAL ABSTRACT****** When a jet of mixed nitrogen or hydrogen atoms and molecules is collected in a beaker of superfluid helium, a gel-like network consisting of small clusters of the atoms and molecules surrounded by very thin layers of solid helium is formed. This porous substance is known as an impurity-helium solid. The clusters contain large concentrations of these atoms (free radicals), which are stabilized against recombination into molecules by the surrounding molecules contained in the clusters as well as the layers of solid helium. Studies will be made of the chemical energy stored in the trapped free radicals, which can be released when they recombine into molecules. Investigations will primarily employ magnetic resonance and optical spectroscopy. Quantum mechanically driven chemical reactions, which can occur even at absolute zero and can lead to exchange between free hydrogen atoms and hydrogen atoms bound in molecules, will be studied. At the very lowest temperatures, the atomic hydrogen free radicals may even undergo Bose-Einstein condensation, an extreme form of quantum behavior that can give rise to superfluidity. Postdocs and students trained in this program will acquire research skills in cryogenics and magnetic resonance, techniques that have wide utility in many areas of science and technology.
This research program will involve studies of hydrogen or nitrogen atoms embedded in molecular matrices consisting of hydrogen or nitrogen molecules, respectively. The matrices can be either bulk molecular solids or porous gels (impurity-helium solids) composed of nanoclusters of the molecular solids, each of which is surrounded by a monolayer or two of solid helium. The resulting matrix isolation of the atomic free radicals stabilizes them against recombination into molecules, allowing them to be studied for many days. Properties of these systems will be investigated at temperatures ranging from 4 K down to 100 mK or less. Magnetic resonance, low frequency magnetic susceptibility and optical spectroscopy will be employed. Studies of magnetic ordering, tunneling exchange chemical reactions, and magnetic relaxation will be performed. A search will be made for possible Bose-Einstein condensation in the embedded hydrogen atoms. The students and postdocs in this program will be well trained in cryogenics and magnetic resonance, both important techniques in science and technology. The field of matrix isolation has many possible variations and unknowns to be explored, giving young people exposure to the excitement of discovery.
