MATRIX ISOLATION OF H AND D ATOMS: PHYSICS AND CHEMISTRY FROM 1.5 TO 0.1 K

Recent work on matrix isolated hydrogen and deuterium atoms in impurity helium condensates (IHC), which consist of nanoclusters of the matrix atoms or molecules (H2, D2, HD, and Kr), is discussed. Continuous wave (CW) and pulsed electron spin resonance (ESR) techniques at 9 GHz have both been employed. The kinetics of exchange tunneling reactions of hydrogen isotopes have been studied at T = 1.35 K. Pulsed ESR has shown that a large fraction of the stabilized atomic free radicals resides on the surfaces of the clusters. High concentrations of hydrogen atoms in IHCs containing Kr atoms and H2 molecules have been attained. Studies of hydrogen atoms embedded in thin H2 films have been conducted at temperatures down to ~0.1 K via ESR at 128 GHz in magnetic fields of 4.6 T. Dissociation of H2 molecules at very low temperatures leads to the accumulation of films containing H atom concentrations ~1019 atoms cm-3. Some remarkable effects have been observed in these samples, including a large departure from the Boltzmann factor for the populations of the two lowest H atom hyperfine states and a complete absence of recombination at the lowest temperatures. 2011 by Pan Stanford Publishing Pte. Ltd. All rights reserved.

MATRIX ISOLATION OF H AND D ATOMS: PHYSICS AND CHEMISTRY FROM 1.5 TO 0.1 K Chapter