Download Pulse and Continuous Wave Electron Spin Resonance Investigations of Atoms

Pulse and Continuous Wave Electron Spin Resonance Investigations of Atoms
in Impurity-Helium Solids
V. V. Khmelenko
Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853, USA
We report pulse and continuous wave (CW) X-band ESR studies of atoms stabilized in impurity-helium
(Im-He) solids. The Im-He solids containing H, D or N atoms as impurities were created by sending a
mixture gases consisting of 1-5% impurity molecules, and the remainder helium atoms, through a radio
frequency discharge into a volume of superfluid 4 He at T =1.5 K. The kinetics of the tunnelling exchange
chemical reactions H+H2 →H2 +H, D+D2 →D2 +D and D+HD→D2 +H in Im-He solids at T =1.25-1.35
K has been studied. From combined CW and pulse ESR studies the information about changes in the
immediate molecular environment of the H and D atoms during the processes of tunnelling reactions
was obtained. Observation of satellite lines in CW ESR spectra which were associated with transitions
involving a spin flip of the electron of a hydrogen or deuterium atom and a simultaneous spin flip of
a proton on neighboring HD or ortho-H2 molecules allows us to calculate the number of protons on
neighboring molecules and their distances to the atoms. The analysis of the modulation effects of the
electron spin echo signals of H and D atoms allows us to determine the number of deuterons on neighboring
molecules and their distances to the atoms. Very high concentrations (∼ 1021 atoms/cm3 ) of stabilized
isotopes of nitrogen atoms (14 N and 15 N) in nitrogen-helium solids were achieved. For the first time the
15
N· · ·15 N spin-pair radicals were observed in Im-He solids with high concentrations of 15 N atoms.
Sorting category: Ae Quantum gases, fluids and solids
Keywords: electron spin resonance, atomic hydrogen, impurity-helium solids
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