SEMIEMPIRICAL CALCULATION OF THE ESCA CHEMICAL-SHIFTS OF THE GROUP IVA ELEMENTS IN A CHEMICAL ENVIRONMENT

The electron spectroscopy for chemical analysis (ESCA) chemical shifts of the C(1s), Si(2p3/2), Ge(3p3/2), Ge(3d5/2), Sn(3d5/2) and Sn(4d5/2 ) levels were considered at the semiempirical level of theory. It was shown that the C(1s) and Si(2p3/2) inner-core energy shifts are satisf actorily accounted for by the SCC-MO method within the relaxation pote ntial (RPf) model. Surprisingly, the more usually used MNDO, AM1 and P M3 methods fail in this regard. The chemical shifts of Ge(3p3/2) and G e(3d5/2) were well described by the PM3/RP(f) scheme, whereas the best method for estimating the Sn(3d5/2) and Sn(4d5/2) inner-core photoion ization changes in a chemical environment was the PM3/GSP model. The l atter makes use of the ground-state potential only. The role of the re laxation energy is discussed and the magnitude of this quantity is int erpreted in a transparent and physically meaningful way by using a par ticular partitioning technique. The use of ESCA shifts and relaxation energies in designing better semiempirical methods is strongly recomme nded.