New low-lying states in NiH: Rotational analysis with the aid of laser-induced dispersed fluorescence spectroscopy

Abstract

In the nonrotating, nonrelativistic limit, the lowest-lying electronic states of the NiH molecule are the Ni( d 9) 2Δ i , 2Π i , and 2Σ + states. These zero-order states are profoundly mixed by the spinorbit and rotational terms in the molecular Hamiltonian. The resultant molecular states form a 10-component 2 D supermultiplet: X 12.5 (≈ 2 Δ 5 2 ), X 21.5 (≈ 2 Δ 3 2 ), W 11.5 (≈ 2 Π 3 2 ), W 20.5 (≈ 2 Π 1 2 ), V 10.5 (≈ 2Σ +) e-parity and f-parity components. Of these, only X 12.5 v″ = 0, 1 and X 21.5 v″ = 0 (formerly X 2 Δ 5 2 v″ = 0, 1 and X 2 Δ 3 2 v″ = 0 , respectively) had been observed previously. We report here new observations of the low-lying states: X 12.5 v″ = 2, X 11.5 v″ = 1, W 11.5 v″ = 0, 1, and from an analysis of a perturbation in X 12.5 v″ = 1, the e-parity component of a V 10.5 level. These new experimental observations will provide a basis for a deperturbation procedure which will yield molecular constants appropriate for comparison with the deperturbed molecular constants predicted by the usual nonrotating, nonrelativistic ab initio calculations. The effective molecular constants for these supermultiplet components, which are derived via traditional fit models for either isolated components or components grouped into Λ- S multiplets, cannot be compared with ab initio calculations or used to compute properties such as Franck-Condon factors or magnetic g-values. The spectroscopic data reported here were obtained by a combination of high resolution grating spectrograph absorption and emission studies, cw laser fluorescence excitation and dispersed fluorescence spectra, and Optical-Optical Double Resonance spectra recorded with two cw dye lasers. The upper levels of the transitions studied include the four states [15.9]2.5, [17.4]2.5, [16.1]1.5, and [17.2]1.5, which were formerly known as the B 2 Δ 5 2 v′ = 0 , and 2 Δ 3 2 v′ = 0, 1 states, respectively.