 The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature ; thus rapidly condensed H2 contains large quantities of the high @-@ energy ortho form that converts to the para form very slowly . The ortho / para ratio in condensed H2 is an important consideration in the preparation and storage of liquid hydrogen : the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid , leading to loss of liquefied material . Catalysts for the ortho @-@ para interconversion , such as ferric oxide , activated carbon , platinized asbestos , rare earth metals , uranium compounds , chromic oxide , or some nickel compounds , are used during hydrogen cooling . 
