Photoelectron Imaging and Spectroscopy of MI₂⁻ (M = Cs, Cu, Au): Evolution from Ionic to Covalent Bonding

Abstract

We report a combined experimental and theoretical investigation of MI(2)(-) (M = Cs, Cu, Ag, Au) to explore the chemical bonding in the group IA and IB diiodide complexes. Both photoelectron imaging and low-temperature photoelectron spectroscopy are applied to MI(2)(-) (M = Cs, Cu, Au), yielding vibrationally resolved spectra for CuI(2)(-) and AuI(2)(-) and accurate electron affinities, 4.52 ± 0.02, 4.256 ± 0.010, and 4.226 ± 0.010 eV for CsI(2), CuI(2), and AuI(2), respectively. Spin-orbit coupling is found to be important in all the diiodide 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 CsI(2)(-) to relatively strong covalent bonding in AuI(2)(-). Both relativistic effects and electron correlation are shown to enhance the covalency in the gold diiodide complex.

Photoelectron spectroscopy and the electronic structure of the uranyl tetrachloride dianion: UO2Cl42−

“…Single-point CCSD(T) energies of the ground and excited states of UO 2 Cl 4 − were calculated at the optimized SR-CCSD(T) geometry of UO 2 Cl 4 2− , generating accurate state-specific SR energies for all the states. The electron detachment energies corresponding to one-electron transitions from the closed-shell ground state of UO 2 Cl 4 2− to the ground and excited states of UO 2 Cl 4 − were obtained using the CASSCF/CCSD(T)/SO approach, 17,[45][46][47][48] which has been shown to generate accurate excitation energies for molecules containing heavy elements. 17,32,49 In this approach, the SO splittings were treated as a perturbation to the SR state energies and were calculated on the basis of CASSCF wavefunctions with the diagonal matrix elements replaced by the individual CCSD(T) state energies.…”

Ab Initio Study of Neutral and Charged Copper Bromide (CuBr) n (+) Clusters (n = 1–6)

“…However, the latter analysis is basisdependent and it is commonly known that one should be cautious when using it especially for atoms with significant overlaps of atomic orbitals [32]. Recently, Wang et al reported an analysis of the bonding in small copper and gold halide complexes, and found a significant covalent character in the metal-halide bonds [33,34].…”

Spectroscopic observation of gold-dicarbide: Photodetachment and velocity map imaging of the AuC2 anion

“…Vibrationally resolved spectra were obtained for the AuH and Au 2 H species, thus demonstrating the usefulness of the technique. MI 2 species (M = Cs, Cu, and Au) have also been investigated using VMI by Wang et al, 22 also in 2010. The images of AuI 2 and CuI 2 gave well-defined vibrational structure and thus could be examined at a high level of detail.…”