The He-I ultraviolet photoelectron spectra of a series of phosphine-substituted organometallic complexes, CO(CO)(2)NOL (L = CO, PMe3, PEt3, PPr3, PBU3, PCy3, PPh3, and P(OMe)(3)) are reported. The first vertical ionization energy of the complexes was found to be 8.75 (CO), 7.85 (PMe3), 7.69 (PEt3), 7.47 (PPr3), 7.49 (PBu3), 7.71 (PCy3), 7.58 (PPh3), and 8.15 eV (P(OMe)(3)) +/- 0.03 eV. Quantum chemical calculations at the HF, DFT (B3LYP), and EOMIP-CCSD levels of theory were employed to interpret both the trends in the series and the most important features of the spectra. Photoelectron spectra of some of the complexes are also reported at He-II photon energy. Intensity changes in the photoelectron bands between He-I and He-II photon energies are discussed on the basis of the orbital compositions.