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| Keywords: Cryogenics 019.jpg A Each type of hydrogen molecule consists of 2 hydrogen atoms spheres connected by a covalent bond connecting bar Light arrows indicated direction of nuclear spin; heavy arrows penetrating spheres show direction of spin axis In orthohydrogen the less stable type at lower temperatures the spin axes point in the same direction; in parahydrogen the axes are directly opposed B Catalyst is a porous ferromagnetic material hydrous ferric oxide through which normal hydrogen 75 percent ortho 25 percent para is made to pass The magnetic field within the small pores one of which is prepresented here dotted lines are lines of magnetic force varies rapidly from one point to another The inhomogenous field interacts with the magnetic moments of the hydrogen atoms and produces internal strains which disturb the balance within the unstable ortho molecules One is shown here at left being symbolically twisted by the action of the field The actual process is governed by quantum rules and the transition to the stable para structure is sudden Another possible mechanism for which the evidence is more definite at higher temperatures is shown symbolically at the right Here the ortho molecules dissociate as they are absorbed on the catalyst surfave and then the atoms can recombine into a stable paramolecule as they are desorbed National Institute of Standards and Technology National Institute of Standards and Technology The images in the Cryogenics Photographic Collection are in the public domain and are not subject to copyright in the United States However please pay special attention to the individual works to make sure there are no copyright restrictions indicated Individual works may require securing other permissions from the original copyright holder Use of the images from NIST Digital Collections is not restricted but a statement of attribution is required Please use the following attribution statement National Institute of Standards and Technology Digital Collections Gaithersburg MD 20899 PD-USGov National Bureau of Standards National Institute of Standards and Technology Cryogenics | ||||
