  We have studied the amorphization process of SnI4 up to 26.8GPa with
unprecedented experimental details by combining Sn and I K edge X-ray
absorption spectroscopy and powder X-ray diffraction. Standards and reverse
Monte Carlo extended X-ray absorption fine structure (EXAFS) refinements
confirm that the SnI4 tetrahedron is a fundamental structural unit that is
preserved through the crystalline phase-I to crystalline phase-II transition
about 7 to 10GPa and then in the amorphous phase that appears above 20GPa. Up
to now unexploited Iodine EXAFS reveals to be extremely informative and
confirms the formation of iodine iodine short bonds close to 2.85{\AA} in the
amorphous phase at 26.8 GPa. A coordination number increase of Sn in the
crystalline phase-II appears to be excluded, while the deformation of the
tetrahedral units proceeds through a flattening that keeps the average I-Sn-I
angle close to 109.5{\deg}. Moreover, we put in evidence the impact of pressure
on the Sn near edge structure under competing geometrical and electronic
effects.
