Ligand-Field Splittings on Core Levels of Main Group Compounds and Metal Surfaces from Photoelectron Spectra

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Abstract
In the last 10 years, ligand-field splittings on core levels of main group compounds (e.g. compounds of Zn, Cd, In, Tl, Xe, I) in the gas phase have been observed using high resolution photoelectron spectroscopy. These splittings on d9 and p5 ion states are analogous to the well-known splittings of valence d levels in transition metals, and are characterized using the usual crystal-field and spin-orbit Hamiltonian. The noncubic C02 term dominates these splittings. The C02 values are sensitive to structure and bonding. For example, C02 increase for R2Zn compounds in the order R=CI < Br < I < Me < Et-just the order of increasing γ donor strength, and the In 4d splitting has been useful in showing that indium trihalides are dimers in the gas phase. Simple calculations are useful for calculating these splittings, especially point charge calculations for the I splittings in alkali iodides. The C02 Hamiltonian term transforms like the nuclear quadrupole Hamiltonian, making it possible to observe the transmission of the ligand field through the atom to the nucleus. Monochromatized synchrotron radiation as a photoelectron source will be important for observing these splittings in more gas phase compounds of a variety of elements, and also for examining core level broadenings on surfaces.

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