Laser spectroscopy of NiI: Ground and low-lying electronic states

Abstract

High-resolution laser-induced fluorescence spectrum of a jet-cooled NiI molecule has been recorded in the near infrared and visible regions. The NiI molecule was produced by reacting laser-ablated nickel atom and methyl iodide (CH3I). Three electronic states have been identified that include the X 2Δ5/2 and two low-lying [13.9] 2Π3/2 and [14.6] 2Δ5/2 excited states. Molecular transition bands (v′,0) of the [13.9] 2Π3/2−X 2Δ5/2 system with v′=0, 4–9, and the (v′,0) bands of the [14.6] 2Δ5/2−X 2Δ5/2 system with v′=0–6 were observed and analyzed. Spectra of isotopic molecules confirmed the assignment of vibrational quantum number of the observed bands. Least squares fit of rotational transition lines yielded accurate molecular constants for the states studied. The bond length r0 measured for the X 2Δ5/2 is 2.3479 Å and the equilibrium bond length, re, for the [13.9] 2Π3/2 and [14.6] 2Δ5/2 are, respectively, 2.4834 and 2.5081 Å. With the use of a molecular orbital energy level diagram, we have examined the electronic configurations that give rise to the X 2Π3/2 ground state for NiF, NiCl, and NiBr, but the X 2Δ5/2 state for NiI. This work represents the first spectroscopic study of the NiI molecule.