Hyperfine structure and Stark effect in the [18.0] 4 - X³Φ₄transition of iridium hydride, IrH and [18.2] 4 - X³Φ₄transition of iridium deuteride, IrD

High resolution spectra of IrH and IrD, with full width at half maximum (FWHM) of ∼0.001 cm^-1, have shown well resolved hyperfine structure due to the nuclear spin, I = 3/2, of ¹⁹³Ir and ¹⁹¹Ir. Analysis of the hyperfine structure in the [18.2] 4 - X³Φ₄transition of ¹⁹³IrD and ¹⁹¹IrD yielded well defined magnetic and quadrupole Ir hyperfine parameters which showed that the ground X³Φ₄state originates predominantly from the two open-shell Ir(5dπ³5dδ³) configuration with a significant contribution from the four open-shell Ir(5dσ5dπ³5dδ³6sσ) configuration. Examination of the Stark effect in the [18.0] 4 - X³Φ₄transition of ¹⁹³IrH yielded electric dipole moments of 1.23(1) D and 0.76(1) D for the ground and excited states, respectively. The hyperfine constants and the dipole moment of the ground state are seen to follow the trend shown by the isovalent molecules, CoF, CoH and IrF.