THE ELECTRONIC-STRUCTURE OF NIH - THE (NI+3D9 2D) SUPERMULTIPLET

A global deperturbation is presented for all electronic states of NiH with T0 values below 0.3 eV. These states form an isolated group and are treated as components of a molecular "supermultiplet" which is derived from a nickel-centered 3d9 electron configuration such as that found in the 2D term of Ni+. Observed term energies for all low-lying states, including some vibrationally excited levels, are used in a least squares fit to the supermultiplet model. A crucial feature of the supermultiplet model is its employment, wherever possible, of atomic angular (e.g., L +/- \L-LAMBDA> = [L (L + 1 ) - LAMBDA (LAMBDA +/- 1)]1/2\L-LAMBDA +/- 1>) and radial (e.g., spin-orbit coupling constants) matrix elements to define and constrain the molecular effective Hamiltonian. A relatively small number of adjustable parameters are required to represent the upsilon = 0 and 1, J = 0.5-11.5 term values in the supermultiplet picture and accurately describe a variety of observations, which include large OMEGA-doublings, unusually large and J, OMEGA, e/f-dependent Zeeman g values, and a symmetry-forbidden (DELTA-LAMBDA = 2) rotational pertubation. The number of independently adjustable parameters required by the supermultiplet model is significantly smaller than a standard 2-DELTA, 2-PI, 2-SIGMA+ deperturbation model. In addition, the fitted deperturbed (i.e., nonrelativistic and nonrotating) molecular constants for the 2-DELTA, 2-PI, 2-SIGMA+ components of the NiH supermultiplet are in better agreement with theoretical descriptions than previous empirical constants taken directly, without deperturbation, from spectra. The fit model also yields an empirical value of the (3d9) sigma approximately 3d10 configuration mixing coefficient, which is relevant to a global understanding of the d9 and d10 states in the homologous NiH, PdH, PtH series of molecules.