Charge transfer complexes of polycyclic aromatic hydrocarbons with alk
ali metal are known to adsorb hydrogen chemisorptively. We investigate
hydrogen uptake effects on the properties of metallic K3C60 by means
of ESR and superconductivity measurements. The introduction of hydroge
n induces a disproportionation reaction, resulting in the generation o
f K6C60 domains which have interstitial sites available for the accomm
odation of dissociated hydrogen atoms. The annealing process makes the
hydrogenated K3C60 homogeneous where small amounts of hydrogen are st
abilized as impurities. Superconductivity is not influenced by hydroge
n uptake.