DETERMINATION OF THE I-2 BOND-LENGTH DISTRIBUTION IN LIQUID, SOLID AND SOLUTION, BY EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE SPECTROSCOPY

A systematic extended x-ray absorption fine structure (EXAFS) study of the structural parameters of the I-2 molecule has been performed for I-2 liquid, solid and in low density gaseous phases, as well as for I- 2 dissolved in organic solvents. Measurements on gaseous HI have also been performed in order to refine the structural analysis, A complex a tomic double-electron excitation background at the I K-edge has been o bserved, A careful data analysis with full statistical evaluation of t he results has indicated undoubtedly that, in condensed phases, the av erage bond length can increase by as much as 0.03 Angstrom with respec t to the free molecule value. The expansion, known to occur from gas t o Liquid, and solid I-2, was confirmed by the present EXAFS analysis w hile in the case of I-2 in solution this is the first determination of the bond length, In particular we find that the bond length increases monotonically while decreasing the ionizing potential of the solute. A Linear correlation between the blue-shift of the optical absorption I-2 band and the increase of the bond length has been found. (C) 1997 American Institute of Physics.