Experimental verification of the distortion overlap in alkali iodide systems

Isomer shift systematics of ¹²⁹I Mössbauer effect in the alkali iodides, solid-argon-matrix-isolated molecules, and crystals show unambiguously that no charge transfer (covalency) is present in these ionic species. The mechanism of distortion overlap is the only mechanism responsible for the enhancement of s-electrondensity along the metal-halogen bond. It is shown that the role of next-nearest-neighbors overlap present in the crystal is of prime importance and overwhelming in the case of LiI. The conclusions derived from the isomer shift and quadrupole coupling data suggest a larger intramolecular distance in the argon matrix as compared to the vapor phase.