OPTICAL-SPECTRA OF NI(CO)(4) AND CR(CO)(6) REVISITED

The electronic absorption spectra of Cr(CO)(6) and Ni(CO)(4) have been studied in detail using multiconfigurational perturbation theory base d on a complete active space wave function (the CASSCF/CASPT2 approach ). Calculated results for both excitation energies and oscillator stre ngths are reported. Based on the calculated results an assignment of t he experimental absorption spectra is proposed. In both cases, the ass ignment is different from any previously published assignments, The mo st striking difference is found for the ligand field excited states in Cr(CO)(6), which are calculated at a much higher wavenumber than sugg ested by the original and the since then generally accepted assignment of the Cr(CO)(6) absorption spectrum by Beach and Gray.(1) This resul t may throw new light upon the role played by the ligand field states in the photochemistry of Cr(CO)(6) and other carbonyl compounds.