MII,IIIspectrum of atomic nickel:Ab initiocalculations

Ab initio calculations of the $3d$ photoionization cross section of ${\mathrm{Ni}}^{+}$ ($3p^{6}3d^9$ ground-state configuration) have been performed using $R$-matrix theory. Their results are discussed in terms of interpretation of $M_{\mathrm{I}\mathrm{I},\mathrm{I}\mathrm{I}\mathrm{I}}$ experimental spectra obtained by several techniques and validity of theoretical approximations. They point out the existence of more or less autoionizing sharp lines series converging to the various $3p$ ionization thresholds, in addition to a broad asymmetric Fano profile. Also, the connection of such calculations with the problem of Auger spectra is emphasized since they bring direct evidence of the importance of coupling the channels when treating the relaxation and broadening effects involved in the interpretation of x-ray photoemission spectra. Our conclusions are in favor of a $3d-4s$ shake-up process involved in the final ionic state $3p^{6}3d^{7}4s$ to explain the existence of the strong satellite (6 eV below the Fermi level) in solid nickel photoemission spectra.