Quasirelativistic calculation of the vibronic spectra of NiH and NiD

Publisher Website
Google Scholar
Abstract
Large a b i n i t i o calculations on the low‐lying 2Δ, 2Π, and 2Σ+ electronic states of NiH have been performed employing a relativistically corrected Hamiltonian. The relative ordering of the unperturbed electronic states is found to be 2Δ<2Σ+<2Π. Diagonal and off‐diagonal spin–orbit matrix elements have been evaluated within the Breit–Pauli approximation and were used to couple the individual vibronic functions. With the exception of 〈2Σ+ 1/2‖H SO‖2Π1 / 2〉, the spin–orbit matrix elements are found to be nearly independent of the internuclear distance. Their magnitude is determined by coupling matrix elements of the components of a pure atomic d 9 configuration. The deflection of the 〈2Σ+ 1/2‖H SO‖2Π1 / 2〉 matrix element from the d 9 limit at shorter bond distances can be attributed to increased admixture of d 1 0 character in the 2Σ+wave function. For NiH the v=0, J=2.5 level of the 2Δ3 / 2 state is calculated at 1014 cm− 1, in excellent agreement with experiments (1012 cm− 1). The lower of the heavily mixed 2Σ+ 1/2 and 2Π1 / 2 combinations with total angular momentum J=2.5 is located at 2279 cm− 1, approximately 150 cm− 1 above the corresponding experimental value. Shifting the 2Σ+ potential curve by −250 cm− 1 brings the calculated levels of the Ω=1/2 system into almost perfect agreement with observed levels averaged over e and f components. The upper, experimentally not yet determined component is predicted at approximately 3655 cm− 1, close to the v=2 level of the 2Δ5 / 2 state. The 2Π3 / 2 v=0, J=2.5 and the 2Δ3 / 2 v=1, J=2.5 levels, located at 2631 and 3091 cm− 1, are considerably mixed. Excitation energies to several higher‐lying vibronic states of NiH and a corresponding analysis of the vibronic spectrum of the NiD isotope are also reported.