The effect of pressure on the absorption spectrum and the crystal structure of anhydrous AmI3

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Abstract
Anhydrous AmI3 was investigated as a function of pressure up to approximately 10 GPa in a diamond anvil cell using absorption spectrophotometric analysis. AmI3 is the only actinide tri-iodide known presently to be dimorphic, and at room temperature and normal pressure there is an appreciable difference between the molecular volumes of each structure. It has been determined that an applied pressure of approximately 2 GPa will convert the rhombohedral form (large molecular volume) of AmI3 to the orthorhombic structure. this structural change with pressure has been interpreted as reflecting relative packing efficiencies in the crystals. This is believed to be the first spectrophotometric observation of a pressure induced phase transition in an actinide compound.