The high-resolution He I photoelectron spectrum of C60 in the gas phase is reported and compared with the photoelectron spectrum of C60as a thin film prepared by vapor deposition (one to three monolayers) on gold. The spectra show low valence ionization bands that are very sharp and well-separated for a molecule of this size, consistent with the highly symmetric truncated icosahedral structure and theoretical calculations. The total band widths of the valence ionizations from the thin film samples are comparable to those from the gas phase species, showing that the electronic interactions between the molecules and with the surface do not significantly influence these measurements of the molecular electronic structure. The gas phase photoelectron spectra also show vibrational fine structure in the first and second ionization bands with spacings that are consistent with the two totally symmetric vibrational modes of C60. The first vertical ionization energy relative to the vacuum level is determined to be 7.61 ± 0.02 eV from these gas phase measurements.
The relationship between the bite angles of cis phosphines and the electron distribution and bonding to the metal is studied by gas phase valence photoelectron spectroscopy. The complexes selected for the electronic structure comparison are cis-Mo(C0)4(PMe3)2, Mo(CO),DMPE (DMPE = 1,2-bis dimethylphosphinotethane), Mo(CO),DMPM (DMPM = bis(dimethy1phosphino) methane), cis-W(CO),(PMe,),, W(CO),DMPE, and cis-W(CO),DMPM. The Mo carbonyl complexes give simple photoelectron spectra with the valence ionizations originating from the phosphine lone pairs bonding to the metals and from the metal d6 configurations. The W complexes give similar spectra, but have an additional elcctronic spin-orbit perturbation. The ionizations from the phosphine lone pairs that donate to the metals in o bond formation show the effects of the different bite angles of the ligands. However, the total interaction and charge distribution of the phosphines with the metals look very similar in each case. The metal-based ionizations also show very similar bonding and charge distribution in each case. The similarity of the cis-(PMe,), and DMPE spectra is interesting in light of the = 15" difference in P-M-P angles. The metal-based ionizations of the DMPM complexes are slightly different from those of the other complexes, primarily because of through-space interactions with the methylene carbon in the phosphine backbone, The similarity in electronic interactions with the metal in these complexes is traced to a twist of the phosphine coordination to the metal which adjusts for the steric or bite angle constraints of the ligands with a minimum effect on the bonding to the metal. This results in slightly bent metal-phosphorus bonds.
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