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

Abstract

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 191IrO–193IrO isotope shifts in the rotational lines, observed at a linewidth of ∼0.006cm−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 191Ir and 193Ir. Analysis of the spectra shows that the hyperfine structure is concentrated in the two excited states with quadrupole coupling constants, eQq0, 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.