The electronic structure of NiH: The {Ni+3d 9 2D} supermultiplet

Abstract

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_±‖LΛ〉=[L(L+1)−Λ(Λ±1)]^1/2‖LΛ±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 v=0 and 1, J=0.5–11.5 term values in the supermultiplet picture and accurately describe a variety of observations, which include large Ω doublings, unusually large and J, Ω, e/f‐dependent Zeeman g values, and a symmetry‐forbidden (ΔΛ=2) rotational pertubation. The number of independently adjustable parameters required by the supermultiplet model is significantly smaller than a standard ²Δ, ²Π, ²Σ⁺ deperturbation model. In addition, the fitted deperturbed (i.e., nonrelativistic and nonrotating) molecular constants for the ²Δ, ²Π, ²Σ⁺ 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)σ∼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.