The He(I) photoelectron spectra of some gaseous 3 d-transition metal dihalides

Abstract

High-temperature He(I) photoelectron spectra of the vapors over a heated mixture of a metal powder and AgX (X = Cl, Br) and of the vapor species (AgCl) 3 and (AgBr) 3 have been obtained. The vapor has been determined to be composed predominantly Of MX 2 (M  Cr, Mn, Fe, Co, Ni) or (CuX) 3 (X = Cl, Br), except over the Ni powder—AgBr mixture where the vapor contains a significant AgBr component. The spectra of (AgCl) 3, (CuCl) 3, and (CuBr) 3 are similar to those published previously. The (AgBr) 3 spectrum is analogous to the (AgCl) 3 spectrum and has three peaks at 9.60, 10.27, and 10.77 eV, assigned to halogen ionizations, and three peaks at 12.59, 13.54, and 14.06 eV thought to arise from Ag 4 d orbitals. Both spin-restricted and spin-polarized overlapping-spheres multiple-scattering Xα calculations have been performed on several electronic configurations of CrCl 2, MnCl 2, FeCl 2, CoCl 2, NiCl 2, and ZnCl 2. Configurations included both high-spin and low-spin occupancy in all molecules, plus δ 3 π 2 σ 0 MnCl 2 and δ 3 π 2 σ 1 CoCl 2. These calculations have been used together with the He(I) spectra and the unpublished He(II) spectra of Potts [23] for MCl 2 (M = Cr, Mn, Fe, Co, Ni) to make ground-state and MO assignments. Assignments for the corresponding dibromides have been made by analogy. It has been shown that spin-polarized calculations are necessary to explain the photoelectron spectra of the molecules which contain unpaired electrons. The assigned ground-state configurations are δ 2 π 2 σ 0 for CrCl 2 and CrBr 2, δ 2 π 2 σ 1 for MnCl 2 and MnBr 2, δ 3 π 2 σ 1 for FeCl 2 and FeBr 2, δ 3 π 3 σ 1 for CoCl 2 and CoBr 2, and δ 4 π 4 σ 0 for NiCl 2. In every case except CoX 2 the assignments represent the configuration showing the lowest total energy. For CoX 2, the assigned configuration is the second lowest in energy, the energy difference between this and the lowest-energy configuration being very small.