Study of the electronic structure of Ni(eta(5)-C5H5)(NO) by variable-photon-energy photoelectron spectroscopy and density functional calculations

Photoelectron spectra, with photon energies varying from 18 to 120 eV, have been measured for Ni(eta(5)-C5H5)(NO). Relative partial photoelectron cross sections and branching ratios have been evaluated for the first three valence ionization bands. He I and He II photoelectron spectra have been remeasured for Ni(eta(5)-C5H5)(NO) and Ni(eta(5)-C5H4CH3)(NO). In the latter case, the fine structure on the first band differs from that in the previously published spectrum. Density functional calculations have been carried out to determine the ionization potentials of the lowest lying states of Ni(eta(5)-C5H5)(NO) as well as the corresponding photoionization cross sections and the resulting branching ratios using the LCGTO-DF and LDKL-DF methods, respectively. Both experimental and theoretical investigations lead to an ion state ordering (2)E(1) < (2)E(2) similar to (2)A(1) < (2)E(1) and an assignment of (2)E(1) states to the first and third bands with the (2)A(1) and (2)E(2) states comprising the second band. This differs from the original assignment in the literature, where the (2)A(1) ionization was assigned to a high-energy shoulder on the first band. The separation of this shoulder from the main band maximum of 0.23 eV (1850 +/- 81 cm(-1)) suggests that it may be caused by excitation of the NO stretching vibration in the ion. The neutral molecule has a NO stretch of 1832 cm(-1); the calculated energies for the neutral molecule and the cation are 1845 and 1911 cm(-1), respectively. Agreement between calculated and experimental ionization energies and good matching of the theoretical and measured branching ratios support the new assignment of the photoelectron spectrum.