Computational molecular spectroscopy for (X)over-tilde(2)Delta NiCN: Large-amplitude bending motion

摘要

Three-dimensional potential energy surfaces for the 2 A electronic ground state of NiCN have been calculated at the MR-SDCI+Q+E-rel/[Roos AND (Ni), aug-cc-pVQZ (C,N)] level of theory together with electric dipole moments and transition moments. From the ab initio data, standard molecular constants have been determined by the second-order perturbation method, rovibronic term values, rotational constants, and dipole moment expectation values have been determined by the variational RENNER program, and averaged structures have been computed with the variational MORBID method. The perturbation method failed because of a severe Fermi resonance between 2 nu(2) and nu(3). The ab initio calculations yield a linear equilibrium structure with r(e)(Ni-C) = 1.8141 angstrom and r(e) (C-N) = 1.1665 angstrom. The zero-point averaged structure, determined as expectation values in terms of MORBID wavefunctions, is bent with [(rho) over bar](0) equivalent to 180 degrees - [angle(Ni-C-N)](0) = 9(5)degrees, [r(Ni-C)](0) = 1.8159 angstrom, and [r(C-N)](0) = 1.1705 angstrom. The bending potential is shallow and gives rise to large-amplitude bending motion. Kingston et al. [C.T. Kingston, AJ. Merer, T.D. Varberg, J. Mol. Spectrosc. 215 (2002) 106-127] have obtained r(0,Omega=-5/2)(C-N) = 1.1591(29) angstrom in LIF experiments, and Sheridan and Ziurys [P.M. Sheridan, L.M. Ziurys, J. Chem. Phys. 118 (2003) 6370-63791 obtained the value 1.1590(2) angstrom from microwave spectra. These experimentally derived r(0,Omega=5/2)(C-N)-vaIues are 'too short' when compared with [r(C-N)](0) but not so seriously short as in the cases of FeNC and CoCN. (c) 2008 Elsevier Inc. All rights reserved.