Core and valence-shell electronic excitation of nickel tetracarbonyl by high-resolution electron energy loss spectroscopy

Abstract

Core (inner-shell) and valence-shell electron energy loss spectra of Ni(CO)4 are compared with corresponding spectra of free CO under kinematic conditions where the spectra are dominated by dipole-allowed transitions. The inner-shell spectra encompass the C 1s, O 1s, and Ni 3p excitation and ionization regions of Ni(CO)4. The C and O 1s spectra of Ni(CO)4 show some major similarities to those of free CO. In particular both the C 1s and the O 1s inner-shell spectra of both molecules exhibit intense 1s → π* and 1s → σ* transitions. For the case of the C 1s → π* transitions vibrational structure is resolved for both Ni(CO)4 and CO. There are also significant differences, however, which are related to the different manifolds of final states available in the two molecules. Tentative assignments are suggested for the Ni(CO)4 spectra using molecular orbital energy level and term value considerations. The implications of the results for studying dπ → pπ back-bonding in transition-metal carbonyl complexes are discussed. © 1989 American Chemical Society.