Combined experimental and theoretical study on low-lying electronic states of CuO−

We present a combined experimental and theoretical study on the electronic structure and bonding characteristics of the CuO− anion. On the experimental side, high resolution photoelectron imaging has allowed the detection of new features of the low-lying states of the CuO−. Supporting MRCI+Q calculations with inclusion of complex spin-orbit coupling effects have yielded complemented assignments of the photoelectron spectra obtained in the present and previous experiments to low-lying spin-orbit mixed states, which also reveal strong multiconfiguration correlation effects in CuO−. Analyses on the experimentally measured photoelectron angular distributions indicate that, the Cu–O bond in the X1Σ+ state can be characterized by mixed ionic and covalent interactions, with the ionic character being more dominant, while the a3П state can be characterized by a typical ionic bond. Our results provide a renewed understanding in the interplay of ionic-covalent bonding characters in the diatomic CuO− anion.