Electronic spectroscopy of iridium containing diatomic molecules

Abstract

This thesis reports the study of molecular and electronic structure of iridium containing diatomic molecules using the technique of laser ablation/reaction with free jet expansion and laser induced fluorescence (LIF) spectroscopy. The iridium containing diatomic molecules studied in this research are iridium phosphide (IrP), iridium boride (IrB) and iridium oxide (IrO). These molecules were produced by the reaction of Ir atoms ablated by a pulsed neodymium-doped yttrium aluminium garnet (Nd:YAG) laser and 1% PH3, 0.5% B2H6 and 6% N2O gases to produce IrP, IrB and IrO molecules respectively. Pulsed tunable lasers: a dye laser and an optical parametric oscillator (OPO) laser system were used to cover the spectral region between 390 and 650 nm in obtaining electronic transitions of the iridium containing diatomic molecules.

The recorded electronic spectra of IrP, IrB and IrO molecules yields information on the bond length and electronic structures. For the IrP molecule, five electronic transitions, namely the [21.2] 3Σ+ – X1Σ+, [21.7]1Σ+ – X1Σ+, [23.6] 0+ – X1Σ+, [23.7] 0+ – X1Σ+ and [23.9] 0+ – X1Σ+ transitions, have been recorded and analyzed. The bond length, r0, and the ΔG1/2 of the ground state of 193IrP molecule was determined to be 1.9928? and 569.77 cm-1 respectively. For the IrB molecule, four new electronic transition systems, namely the [18.8]3Δ3 – X3Δ3, [21.1]3Φ4 – X3Δ3, [22.8]3Φ3 – X3Δ3 and [22.4]1Φ3 – a1Δ2 transitions, were observed and analyzed rotationally. The bond lengths, r0, of the upper states of 193IrB were determined to be within 1.72 and 1.80?. For the IrO molecule, five electronic transitions from two different lower states were recorded and analyzed, namely the [17.6] 2.5 – X2Δ5/2, [17.8] 2.5 – X2Δ5/2, [21.5] 2.5 – X2Δ5/2, [22.0] 2.5 – X2Δ5/2 and [21.9] 3.5 – Ω = 3.5 transitions. The ground state of IrO has been confirmed to be 25/2. The bond length, r0, and the ΔG1/2 of the ground state of 193IrO molecule was determined to be 1.726 A and 900.00 cm-1 respectively. For all the transitions observed, rotationally-resolved transition lines were fit to theoretical models to obtain molecular constants for both the upper and lower electronic states. Typical molecular transition linewidths obtained was larger than 0.1cm-1, which is likely to be due to unresolved hyperfine structure in the rotational lines. In addition, the observation of isotopic spectrum confirmed the assignment of vibrational quantum number. Molecular and electronic structures of these iridium containing diatomic molecules were discussed using a simple molecular orbital theory.