Ab initiostudy of electronic properties in free and matrix-isolated iron dihalides

Abstract

Ab initio Hartree-Fock calculations are performed in the molecular ${}_{}{}^5{}_{}{}^{}\mathrm{\Delta }_{\mathrm{g}}^{}{}_{}{}^{}$, ${}_{}{}^5{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$, and ${}_{}{}^5{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ states of the dihalides ${\mathrm{FeCl}}_2$ and ${\mathrm{FeBr}}_2$ at experimental and geometry-optimized atomic separations. Molecular-term energies, ionization energies, bond energies, electric-field gradients (EFG), and electron densities ρ(o) (the latter two quantities at the iron nucleus) are evaluated and compared with experiment. Electron-correlation corrections and basis-set effects on the energies, EFG, and ρ(0) are studied. The relative isomer shift of noble-gas-matrix-isolated ${\mathrm{FeCl}}_2$ and ${\mathrm{Fe}}^0$ is analyzed on the basis of electron densities calculated in ${\mathrm{FeCl}}_2$–noble-gas and ${\mathrm{Fe}}^0$–noble-gas clusters.