A THEORETICAL STUDY OF NiCN IN THE $^2\Delta$ ELECTRONIC GROUND STATE

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2006

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Ohio State University

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The three-dimensional potential energy surface of $\tilde{X}\,^2\Delta_i$ NiCN has been calculated {\it ab initio} at the MR-SDCI+Q+$E_{\rm rel}$/[Roos ANO (Ni), aug-cc-pVQZ (C, N)] level of theory. The equilibrium geometry derived from this surface is linear with $r_{\mathrm e}$(Ni-C) $=$ 1.814 [1.8292(28), 1.8293(1)] \AA \ and $r_{\mathrm e}$(C-N) $=$ 1.167 [1.1591(29), 1.1590(2)] \AA, where the values in brackets are $r_0$ values for the ground $\Omega=5/2$ spin-substate determined experimentally by Kingston \textit{et al}.}., \textbf{215}, 106 (2002).} and Sheridan \textit{et al}.,}., \textbf{118}, 6370 (2003).} respectively. From the electronic structure given in terms of natural orbitals, and the Mulliken population} of +0.83 on Ni, we conclude that the Ni-C bond is basically ionic but less ionic than those of FeNC and CoCN. The electron from Ni goes into the Ni-mediated CN $\sigma$* orbital, giving the electron distribution Ni$^{+0.8}$(CN)$^{-0.8}$. The $3d$-$\pi$* backbonding is not observed. Molecular constants determined from the \textit{ab initio} potential energy surface by perturbation methods and in variational calculations will be reported: For example, $\omega_1$ = 2198 \wn, $\omega_2$ $=$ 254 \wn, and $\omega_3$ $=$ 511 \wn. A severe Fermi resonance between $2\nu_2$ and $\nu_3$ is expected. A spin-orbit interaction scheme including the \textit{ab initio} predicted spin-orbit coupling constant $A_\mathrm{SO}$ $=$ $-$613 \wn}. the unperturbed $A_\mathrm{SO}$-value of $-$594.2(5) \wn\ for $X\,^{2}\Delta$ NiH; J. A. Gray, M. Li, T. Nelis, and R. W. Field, \textit{J. Chem. Phys}., \textbf{95}, 7164 (1991).} will be presented.

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Author Institution: Research Institute for Computational Sciences, National; Institute of Advanced Industrial Science and Technology,; 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan; Theoretische Chemie, Bergische Universitat,; D-42097 Wuppertal, Germany

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