The Rare Earth-Hydrogen Compounds

The rare earth metals form hydrides readily and a number of studies have been performed on these materials (143). The dihydrides of the rare earths form in CaF2-type structure. The crystal field problem has been applied to characterize the fundamental role of hydrogen in these compounds (144-149). The information accumulated for several dihydrides seems to favor the anionic model, namely, that hydrogen accepts an electron to become negatively charged. We will illustrate the results on PrH2 and ErH2. 

Inverse susceptibility results of PrH2 shown in Fig. 21 are compared with the values calculated [Eq. (25)] using the spectrum shown in Fig. 22 for anionic hydrogen and an overall crystal field splitting of 657 K. The excellent agreement between experiment and theory seems to support the anionic model for hydrogen with Ts triplet 

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