Ab-initio potential energy curves of valence and Rydberg electronic states of the PO radical

This paper reports a theoretical study of the electronic states of PO radical. Highly correlated ab initio methods were used for mapping the potential energy curves. Internally contracted multi-reference configuration interaction method with the augmented correlation-consistent basis set (aV5Z) has been employed to carry out the study. After the nuclear motion treatment, the spectroscopic constants and the vibrational energy levels of the doublet and quartet electronic states are determined. The calculated values have been found in a good agreement with the existing experimental and theoretical results. The spin-orbit couplings between interacting states were also determined in the region where the crossings of the potential energy curves occurs. These couplings are capable to induce predissociation processes involving quartet states and producing P and O atoms at their ground and low lying excited electronic states. The theoretical vibrational spectrum was predicted using the Franck Condon factors and the transition moments integrals. The calculated spectrum shows intense peaks involving the Rydberg states in complete accordance with the experiment.