https://doi.org/10.1140/epjb/e2014-50282-2
Regular Article
Electron exchanges in nuclear spin conversion of hydrogen physisorbed on diamagnetic insulators
1 Matériaux et Phénomènes Quantiques –
Université Paris 7 Denis Diderot and CNRS UMR 7162, Case 7021, 75205
Paris Cedex 13,
France
2 Departamento de Física – Universidade
Federal de São Carlos, Caixa Postal 676, CEP 13565-905, São Carlos,
Brasil
a
e-mail: ernest.ilisca@gmail.com
Received:
3
May
2014
Received in final form:
29
June
2014
Published online:
20
October
2014
Models are provided and discussed to interpret new experiments on the ortho-para conversion of hydrogen “physisorbed” on dielectric and diamagnetic surfaces. Electro-static and dynamical molecule-surface interactions complemented by hyperfine contacts are shown to be generally more effective than the magnetic ones. Coulomb repulsion induces exchanges of molecular and surface electrons and excites triplet spin states which are effective in the angular momenta transfers to the catalyst. The conversion time is obtained as the square of a ratio of two energies: the exchange and excitation ones. The main channel is found composed of triplet excitations of the order of the eV, induced by molecule-surface exchanges of about a hundred of meV. It explains the zinc and oxygen rates of about one minute observed on the MOF samples as well as the about ten times slower ones on the ASW. The same mechanism is also shown to occur in the transient regime, but faster. Finally it explains also the conversion of a few hours observed for interstitial hydrogen in silicium by transitions to the conduction band induced by about 10 meV electron exchanges. The molecule-surface orbital geometries of the MOF and ASW configurations are displayed and the quantum path when unfolded exhibits the successive broken symmetries.
Key words: Solid State and Materials
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2014