Near-infrared laser spectroscopy of NiI.

Laser-induced fluorescence spectrum of NiI in the near infrared region of 714–770 nm has been recorded. Seven bands belonging to three electronic transition systems were observed and analyzed: the (0,0), (1,0), and (2,0) bands of [13.3] ²Σ⁺-A ²Π_3/2 system; the (1,1) and (0,1) bands of [13.9] ²Π_3/2-X ²Δ_5/2 system; and the (0,0) and (1,0) bands of [13.9] ²Π_3/2-A ²Π_3/2 system. Spectra of isotopic molecules confirmed the vibrational quantum number assignment of the observed bands. Least-squares fit of rotationally resolved transition lines yielded accurate molecular constants for the v=0–2 levels of the [13.3] ²Σ⁺ state, the v=0 level of the A ²Π_3/2, and the v=1 level of the X ²Δ_5/2 state. The vibrational separation, ΔG_1/2, of the ground state was measured to be 276.674 cm-1. With the observation of the [13.9] ²Π_3/2-A ²Π_3/2 and [13.9] ²Π_3/2-X ²Δ_5/2 transitions, we accurately determined the energy separation between the A ²Π_3/2 and the X ²Δ_5/2 to be 163.847 cm-1. This confirms that the order of the A ²Π_3/2 and X ²Δ_5/2 states in NiI is reversed when compared with other nickel monohalides. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]