Laser spectroscopy of NiBr: Ground and low-lying electronic states.

Four electronic states of NiBr have been studied using the technique of laser vaporization/reaction with supersonic cooling and laser induced fluorescence (LIF) spectroscopy. NiBr molecules were produced by reacting laser ablated nickel atoms and ethyl bromide (C[sub 2]H[sub 5]Br). High resolution LIF spectrum between 724 and 810 nm was recorded, which consists of the (2,0), (1,0), and (0,0) bands of the [13.2] ²Π[sub 3/2-]-X²Π[sub 3/2] system and the [13.2] ²Π[sub 3/2]--A ²Δ[sub 5/2] system, and also the (v,0) with v = 0-4 bands of the [12.6] 2Σ[sup +]-X²Π[sub 3/2] system. Spectra of four isotopic molecules: [sup 58]Ni[sup 79]Br, [sup 58]Ni[sup 81]Br, [sup 60]Ni[sup 79]Br, and [sup 60]Ni[sup 81]Br were observed and analyzed. Least squares fit of rotationally resolved transition lines yielded accurate molecular constants for the X²Π[sub 3/2], A ²Δ[sub 5/2], [12.6] 2Σ[sup +], and [13.2] ²Π[sub 3/2] electronic states of NiBr. The bond length, r[sub 0], measured for the X²Π[sub 3/2] and A ²Δ[sub 5/2] states is 2.19628 and 2.16445 Å, respectively. A molecular orbital diagram has been constructed to explain the four observed electronic states. This work represents the first high-resolution spectroscopic study of NiBr. [ABSTRACT FROM AUTHOR]