Pressure-Induced Reverse Reaction of the Photochemical Decomposition of Germanium Tetraiodide Molecular Crystal

GeI4 molecular crystal and its solution in cyclohexane were irradiated by lasers of different wavelengths to investigate the critical wavelength for photochemical decomposition of GeI4. We have observed that 633 nm laser can photochemically decompose GeI4, exceeding the previously reported wavelength limit of 514 nm. XPS spectra indicate that GeI4 is photochemically decomposed into Ge2I6 and I-2; unlike GeBr4, Ge2+ (GeI2) cannot be found in the photochemical reaction products. Raman spectra measurement of GeI4 under high pressure up to 24 GPa show that Raman signals of Ge2I6 and I-2 vanish at 0.5 to 1.7 GPa. This finding clearly shows that high pressure can effectively reverse the photochemical decomposition of GeI4 and influence the direction of the solid-state reaction, which is usually found on gas-phase reactions.