High-level relativistic MRCI+Q calculations on excited states of the SbI molecule.

• Total 34 Λ-S states of SbI are accurately characterized at the MRCI+Q level. • The SOC effect makes 34 Λ-S states split into 74 Ω states. • Transition mechanisms of a1Δ-X3Σ− and b1Σ+-X3Σ− are illustrated. • The SOC effect is indispensible for accurate spectroscopic determinations of SbI. In this work, all-electron ab initio calculations on the SbI molecule have been carried out with the multi-reference configuration interaction plus the Davidson correction (MRCI+Q) method. In the calculations, total 34 Λ-S states have been obtained for the first time. From calculated PECs, the derived spectroscopic constants well agree with available experimental values. It should be mentioned that A3Π is typically repulsive, which much differs from the cases of lighter analogs SbX(X=F, Cl, and Br). The molecule is expected to possess a strong spin-orbit coupling effect because both Sb and I atoms have a large atomic number (Z). Therefore, this effect is included by using the state interaction method. As a result, there are 74 Ω states generated from Λ-S states. For X3Σ−, the determined energy splitting of 980 cm−1 is in good agreement with the measured value of 965 cm−1. The adiabatic excitation energy T e of b1Σ+ is greatly improved after considering the SOC effect. Transition properties of SbI are evaluated. The obtained results demonstrate that SOC effects have a great impact on the transitions a1Δ-X3Σ− and b1Σ+-X3Σ−. Both transitions borrow transition dipole moments (TDMs) from spin-allowed Λ-S transitions. The radiative lifetimes of a1Δ and b1Σ+ are determined to be 2.28 ms and 96.84 μs, respectively. [ABSTRACT FROM AUTHOR]