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 photoele ctron cross sections and branching ratios have been evaluated for the first three valence ionization bands. He I and He II photoelectron spe ctra have been remeasured for Ni(eta(5)-C5H5)(NO) and Ni(eta(5)-C5H4CH 3)(NO). In the latter case, the fine structure on the first band diffe rs from that in the previously published spectrum. Density functional calculations have been carried out to determine the ionization potenti als of the lowest lying states of Ni(eta(5)-C5H5)(NO) as well as the c orresponding photoionization cross sections and the resulting branchin g ratios using the LCGTO-DF and LDKL-DF methods, respectively. Both ex perimental and theoretical investigations lead to an ion state orderin g (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 a ssignment in the literature, where the (2)A(1) ionization was assigned to a high-energy shoulder on the first band. The separation of this s houlder from the main band maximum of 0.23 eV (1850 +/- 81 cm(-1)) sug gests that it may be caused by excitation of the NO stretching vibrati on in the ion. The neutral molecule has a NO stretch of 1832 cm(-1); t he calculated energies for the neutral molecule and the cation are 184 5 and 1911 cm(-1), respectively. Agreement between calculated and expe rimental ionization energies and good matching of the theoretical and measured branching ratios support the new assignment of the photoelect ron spectrum.