Metallization and structural transformation of iodine under pressure: A microscopic view

Elemental iodine has been studied by ${}_{}{}^{129}{}_{}{}^{}\mathrm{I}$ Mössbauer effect at 4 K to pressures of 30 GPa in a diamond anvil cell. Its structural transformations leading to metallization have been determined by the quadrupole interaction. At P≥16 GPa an ${\mathrm{I}}_2$-${\mathrm{I}}_2$ zigzag chain is formed leading to its metallic behavior and at P≥21 GPa the formation of a quasi two-dimensional system is observed. Up to 30 GPa the $1_2$ molecule remains the building block of the high-pressure structural modifications.