Revisiting the nature of the ZnO ground state: Influence of spin–orbit coupling

Abstract

Relativistic calculations of the low-lying electronic states of the ZnO molecule are performed for the Λ–Σ states, 1Σ +, 1Π, 1Δ, 3Π and 3Σ −, at the CCSD(T) or MRCI level, using scalar relativistic energy-consistent pseudopotentials, and the EPCISO method for spin–orbit CI coupling. The ZnO ground state is assigned to 0 + symmetry and has 1Σ + character around the equilibrium region. The spectroscopic constants ( r e , ω e ) of the 0 + ground state are in good agreement with experimental results. Interpenetration of the vibrational levels of the two lowest 0 + states is also shown.