| Popis: |
The ground state of the linear ${\mathrm{NiN}}_{2}$ cluster is found, from generalized valence-bond configuration-interaction calculations, to be a $^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ state with a short Ni--N distance of 1.64 A\r{} and a Ni--${\mathrm{N}}_{2}$ dissociation energy of 0.8 eV. In this $^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ state near the calculated equilibrium internuclear distance, the electronic wave function may be characterized as arising from a significant admixture of the Ni 3${d}^{10}$ configuration, and the bonding of the ${\mathrm{N}}_{2}$ molecule to the Ni atom may be characterized as ${\mathrm{N}}_{2}$ \ensuremath{\sigma} donation and Ni 3d\ensuremath{\pi} backward donation. Low-lying excited states ${(\mathrm{}}^{3}$${\ensuremath{\Sigma}}^{+}$, $^{3}\mathrm{\ensuremath{\Delta}}$, and $^{3})$ arising from the Ni 3${d}^{9}$4${s}^{1}$ configuration are also studied. Mulliken population analyses, dipole moments, and vibrational and photoemission properties are calculated. Parallel calculations are also performed for the linear NiCO molecule. The $^{1}\mathrm{\ensuremath{\Sigma}}^{+}$ states of both ${\mathrm{NiN}}_{2}$ and NiCO are good models for the chemisorption of ${\mathrm{N}}_{2}$ and CO on a Ni surface, with regard to the downward shift of the molecular stretching frequency in the interacting systems, the photoemission satellite structure, and the orientation of the dipole moments (with a net electron transfer from Ni to ${\mathrm{N}}_{2}$ or CO). |
