Electronic spectroscopy and electronic structure of diatomic IrSi

The optical spectrum of diatomic IrSi has been investigated for the first time, with transitions observed in the range from 17,178 to 23,858 cm(-1) (582-419 nm). A rich spectrum has been recorded, consisting of 14 electronic band systems and a number of unclassified bands. Thirty-one bands have been investigated with rotational resolution, allowing the ground state to be identified as X(2)Δ5∕2 arising from the 1σ(2)1π(4)2σ(2)1δ(3)3σ(2) configuration. The ground X(2)Δ5∕2 state is characterized by ΔG1∕2 = 533 cm(-1) and r0 = 2.0899(1) Å for the more abundant isotopic form, (193)Ir(28)Si (57.8%). The measured excited electronic states have equilibrium bond lengths ranging from 2.17 to 2.25 Å and vibrational frequencies ranging from 365 to 452 cm(-1). Ab initio calculations were also carried out on the molecule using the complete active space self-consistent field and multistate complete active space second-order perturbation theory methods, with relativistic and spin-orbit effects included through the restricted active space state-interaction with spin-orbit coupling method. The calculated ground state agrees with experiment, and a large number of excited states lying within 20,000 cm(-1) of the ground state are reported.