Theory of ortho-para conversion in hydrogen adsorbed on metal and paramagnetic surfaces at low temperatures

Journal Article · Wed Feb 15 00:00:00 EST 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.39.3104· OSTI ID:6548642

Yucel, S

In order to explain the experimental results on Cu(100), Ag(111), Ag thin films, graphite, and H/sub 2/ bubbles in Cu, the ortho-para conversion rates of H/sub 2/ and D/sub 2/ adsorbed on metal and paramagnetic surfaces at low temperatures have been considered. The conversion rates due to magnetic dipole-dipole, Fermi contact, and spin-orbit interaction between the conduction electrons, and nuclear spins of H/sub 2/ (D/sub 2/) are calculated to elucidate the role of the metal surface. Although the rates on clean metal surfaces are found to be too slow to account for the observed rates on Ag, they may explain the catalytic conversion on H/sub 2/ bubble surfaces at 1.3 K. Additionally, effects of impurities and defects on the surface are investigated by calculating the conversion rate in two-dimensional solid D/sub 2/ (H/sub 2/) by emission of one (two) phonon(s). Fast conversion rates observed on Ag and graphite surfaces as well as on the surfaces of H/sub 2/ bubbles may be accounted for by paramagnetic impurities or defects. On Grafoil, both in (..sqrt..3 x ..sqrt..3)R30/sup 0/ commensurate and incommensurate solid phase, a temperature-independent conversion rate is predicted if the mobility of the molecules is high enough to prevent concentration gradients.

• Research Organization: Department of Physics, Syracuse University, Syracuse, New York 13244
• OSTI ID: 6548642
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Vol. 39:5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
COPPER
SORPTIVE PROPERTIES
DEUTERIUM
CHEMISORPTION
ROTATIONAL STATES
GRAPHITE
HYDROGEN
SILVER
CATALYSIS
CRYSTAL DEFECTS
EQUILIBRIUM
IMPURITIES
ISOTOPE EFFECTS
PARAMAGNETISM
PHONONS
SPIN EXCHANGE
SPIN ORIENTATION
TEMPERATURE DEPENDENCE
ULTRALOW TEMPERATURE
CARBON
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
ELEMENTAL MINERALS
ELEMENTS
ENERGY LEVELS
EXCITED STATES
HYDROGEN ISOTOPES
ISOTOPES
LIGHT NUCLEI
MAGNETISM
METALS
MINERALS
NONMETALS
NUCLEI
ODD-ODD NUCLEI
ORIENTATION
QUASI PARTICLES
SEPARATION PROCESSES
SORPTION
STABLE ISOTOPES
SURFACE PROPERTIES
TRANSITION ELEMENTS
400202* - Isotope Effects
Isotope Exchange
& Isotope Separation