PNNL

Abstract

We report??a combined experimental and theoretical investigation on MI2 – (M = Cs, Cu, Ag, Au) to explore the chemical bonding in the group IA and IB di-iodide complexes. Both photoelectron imaging and low-temperature photoelectron spectroscopy are applied to MI2 – (M = Cs, Cu, Au), yielding vibrationally resolved spectra for CuI2 – and AuI2 – and accurate electron affinities, 4.52 ± 0.02, 4.256 ± 0.010, and 4.226 ± 0.010 eV for CsI2, CuI2, and AuI2, respectively. Spin-orbit coupling is found to be important in all the di-iodide complexes and ab initio calculations including spin-orbit effects allow quantitative assignments of the observed photoelectron spectra. A variety of chemical bonding analyses (charge population, bond order, and electron localization functions) have been carried out, revealing a gradual transition from the expected ionic behavior in CsI2 – to strong covalent bonding in AuI2 –. Both relativistic effects and electron correlation are shown to enhance the covalency in the gold di-iodide complex.