Rotational and hyperfine structure in the [17.6]2.5–X2.5 and [23.3]2.5–X2.5 transitions of iridium monoxide, IrO

Laser induced fluorescence spectra of two electronic transitions, [17.6]2.5–X2.5 and [23.3]2.5–X2.5, of IrO have been obtained at high resolution by using a single mode ring dye laser to excite IrO molecules in a laser-ablation molecular beam source. The 191 IrO– 193 IrO isotope shifts in the rotational lines, observed at a linewidth of ∼0.006 cm −1 FWHM, established the vibrational assignment of the [23.3]2.5–X2.5 band as 1–0 and confirmed the previous 0–0 assignment of the [17.6]2.5–X2.5 band. The higher J rotational lines of both transitions are observed to split into closely spaced doublets resulting from quadrupole hyperfine structure caused by the I = 3/2 nuclear spin in 191 Ir and 193 Ir. Analysis of the spectra shows that the hyperfine structure is concentrated in the two excited states with quadrupole coupling constants, eQq 0 , of −0.0463(15) cm −1 and −0.0278(18) cm −1 for the [17.6]2.5 and [23.3]2.5 states respectively.