Computational investigation by ab initio methods of the spectroscopic characteristics of hafnium monosulfide.

The lowest-lying electronic states of HfS molecule have been described by using the theoretical ab initio methods, state-averaged full valence complete active space self-consistent field (SA-CASSCF) and multireference configuration interaction with single and double excitation (MRCI-SD). These calculations have predicted 22 electronic states below 40,124 cm. The unobserved states [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] have been explored for the first time. The potential energy curves (PECs) have been constructed, and the term energy values at equilibrium T, vibrational constants ω, and ωχ have been calculated for all predicted states. Also, the permanent dipole moments (PDMs) as well as the transition dipole moments (TDMs) have been examined and presented as function of the internuclear distance R. In addition, by employing the spin-orbit coupling in the calculations, 43 Ω components have been obtained below 40,645 cm. The observed states, named AΣ and BΠ, have been assigned respectively as [Formula: see text] and [Formula: see text] of [Formula: see text]. All the calculated spectroscopic constants are found in good agreement with the experiment.