EFFECT OF IONIC LATTICES ON ELECTRONIC STRUCTURES OF POLYATOMIC IONS .2. SULPHATE

The effect of the electrostatic environment of the lattice upon the electronic structure of the sulphate ion is studied by carrying through VESCF calculations of the free sulphate ion and the ion in K2SO4, CaSO4 and BaSO4. The ion is treated as a 24 electron system, the basis functions being oxygen 2p, sulphur 3 s and 3 p orbitals. The effect of the lattices is to increase the electron population on the sulphur at the expense of the oxygen populations. Oxygens that are crystallographically inequivalent are found to vary perceptibly in net charge. The lattices are also found to lead to a pronounced lowering in the total electronic energy of the anion and to more negative bond energy values for all SO bonds. The most interesting prediction is of a measurable splitting of degenerate excited spectroscopic states of the ion in the lattices. In particular splittings of several hundred wavenumbers for the longest wavelength 1A1→1T2 band, differing for each of the lattices, are predicted. Comparisons of these predictions with observation could provide a valuable testing of various wave functions for sulphates, and indeed other polyatomic ions in general. © 1968 Springer-Verlag.