Electronic Transitions of Iridium Monoxide: Ground and Low-Lying Electronic States

The electronic transition spectrum of IrO in the spectral region between 448 and 650 nm has been recorded and analyzed using laser vaporization/reaction free jet expansion and laser induced fluorescence spectroscopy. The IrO molecule was produced by reacting laser-ablated iridium atoms with N₂O seeded in argon. Five electronic transition systems, namely, the [17.6]­2.5 – X²Δ_5/2, [17.8]­2.5 – X²Δ_5/2, [21.5]­2.5 – X²Δ_5/2, [22.0]­2.5 – X²Δ_5/2, and [21.9]­3.5 – Ω = 3.5 systems were identified. Transition lines of both the ¹⁹¹IrO and ¹⁹³IrO isotopes were observed and analyzed. IrO was determined to have a X²Δ_5/2 ground state. A least squares fit of the measured rotational lines yielded molecular constants for the ground and low-lying electronic states. A molecular orbital energy level diagram has been used to help with the assignment of the observed electronic states.