Ab initio study of electronic properties in free and matrix-isolated iron dihalides.

Abstract

Ab initio Hartree-Fock calculations are performed in the molecular $^{5}\mathrm{\ensuremath{\Delta}}_{\mathrm{g}}$, $^{5}\mathrm{\ensuremath{\Pi}}_{\mathrm{g}}$, and $^{5}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$ 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 \ensuremath{\rho}(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 \ensuremath{\rho}(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.