We report an ab initio study on the spectroscopy of the open-shell diatomic molecule yttrium
oxide, YO. The study considers the six lowest doublet states, X2Σ+, A′ 2Δ, A2Π, B2Σ+,
C2Π, D2Σ+, and a few higher-lying quartet states using high levels of electronic structure
theory and accurate nuclear motion calculations. The coupled cluster singles, doubles, and
perturbative triples, CCSD (T), and multireference configuration interaction (MRCI) methods
are employed in conjunction with a relativistic pseudopotential on the yttrium atom and a …