DENSITY-FUNCTIONAL CALCULATIONS OF EXCITATION-ENERGIES AND OSCILLATOR-STRENGTHS FOR C1S-]PI-ASTERISK AND O1S-]PI-ASTERISK EXCITATIONS AND IONIZATION-POTENTIALS IN CARBONYL-CONTAINING MOLECULES

Theoretical calculations of C1s --> pi* and O1s --> pi* excitation energies and oscillator strengths together with C1s and O1s ionization potentials in various carbonyl containing molecules have been performed. We employed the DF-LCAO method, with a DZP-STO basis set. Excitation and ionization energies are calculated by the transition state approach, and are more properly discussed as shifts with respect to CO. Comparison of the present results with accurate ab initio and experimental data available for free CO demonstrates the validity of such an approach. The other systems considered range from formylic fluorinated compounds (H2CO, HFCO and F2CO) to transition metal carbonyls (Cr(CO)(6), Mo(CO)(6), Fe(CO)(5), Mn(CO)(5)Br, Mn(CO)(5)H and Ni(CO)(4)) and model molecules (NiCO, PdCO and PtCO). Particular attention is devoted to quantitative considerations about backbonding and to the capability of the excitation intensity to map the pi* ground state orbitals. Comparison of the present theoretical results with experimental data demonstrates the high reliability of the method employed, which is able to correctly predict small effects (small energy shifts and differential relaxation). Some discrepancies in oscillator strengths are reasonably ascribed to experimental normalization errors.