Assignment of the valence molecular orbitals of CpPtMe₃ and Me₂Pt(COD) using variable-energy photoelectron spectra

High-resolution variable-energy photoelectron spectra are reported for the upper valence band region of CpPtMe₃ (Cp = η⁵-C₅H₅) and Me₂Pt(COD) (COD = 1,5-cyclooctadiene) for photon energies between 21 and 100 eV. Xα-SW results on the CpPtMe₃ valence levels arc also reported as the basis for the spectral assignment. Experimental and theoretical branching ratios are in good agreement with the -SW assignment but are inconsistent with the previous Fenske-Hall assignment for the CpPtMe₃ valence ionizations. Contrary to the Fenske-Hall assignment, our present results strongly indicate that the nonbonding Pt 5d orbitals are not the HOMO‧s and have higher ionization potentials than several Pt-L orbitals. Comparisons of the observed and calculated branching ratios also confirm a previous Xα-SW assignment for the Me₂Pt(COD) valence ionizations. Intensity changes of the ionization bands for the two molecules as a function of photon energy are largely dependent on the relative values of the Pt 5d and C 2p atomic cross sections (the Gelius model). There are no obvious resonance enhancements of any of the cross sections.