HYDROGEN ISOTOPE EQUILIBRATION ON GADOLINIUM FILMS

Films of gadolinium evaporated at 10−10 torr have been examined as cata-lysts for the pH2, oD2 and H2 + D2 reactions, at pressures c. 1 torr and tempera-tures 77—450°K. Hydrogen absorption occurs and lowers the catalyst activity, but reproducible results were obtained on the films stabilised at an overall com-Position of about GdH, which were probably a mixture of Gd and defect GdH2 phases. At higher temperatures, viz. 273 °K, all three reactions, which have a similar rate to hydrogen absorption, probably go through the simple dissocia-tion-recombination of H2, the Bonhoeffer-Farkas mechanism. At low temperatures, 77 °K, this may change over to a molecule-adsorbed atom exchange mechanism for H2 + D2, but the pH2, oD2 isomerisation go at the same rate (1000 xH2 + D2 rate) by a paramagnetic mechanism invokedby the unpaired f electrons, atomic moment 7.55 BM. A comparison with calculated rates for the three variants a) collision, b) Vibration over a strongly adsorbing site, c) surface translation, suggests b) as most likely. The conversion rate for pH2 at 77 °K is less than that of oD2, which is anomalous. A similar result may hold for Ni films, in contrast with Ni wires where c) gives a better fit. The failure to observe a magnetocatalytic effect at the Curie point of Gd, 293 °K, may be due to the effect of absorbed (and perhaps adsorbed) hydrogen in bonding the conduction (ds2) electrons responsible for the ferromagnetic coupling of moments in this metal. © 1969, Walter de Gruyter. Alle Rechte vorbehalten.