Accurate potential energy curves and spectroscopic properties of the 27 Λ-S states and 73 Ω states of the PO radical

The potential energy curves (PECs) were calculated for the 27 Lambda-S states and 73 Omega states of PO radical. The calculations were done using the CASSCF method, which was followed by the internally contracted multireference configuration interaction (icMRCI) approach. To improve the quality of PECs, core-valence correlation and scalar relativistic corrections as well as Davidson correction were included. Of the 27 Lambda-S states, the 1(6) Sigma(+) state was repulsive at any case. The 1(4) Phi and 1(6)Pi states were bound, but they became repulsive with the spin-orbit coupling (SOC) effect accounted for. The 3(4)Sigma(+), a(4)Pi, C-2 Delta, D-2 Pi, 1(4)Delta, 1(2)Phi, 1(6)Sigma(+) and 1(6)Pi states were inverted with the SOC effect included. The F-2 Sigma(+) state had double wells. The avoided crossings existed between the B-2 Sigma(+) and F-2 Sigma(+) states, the F-2 Sigma(+) and 3(2)Sigma(+) states, the C'(2)Lambda and 2(2) Lambda states, the 1(4) Lambda and 2(4) Lambda states, the 2(4) Lambda and 3(4) Lambda states, the 2(4) Pi and 3(4) Pi states and the 3(4) Pi and 4(4) Pi states. The c(4) Sigma(+), 2(4)Sigma(+), 3(4)Sigma(+), 3(4)Pi, 4(4)Pi, 5(4)Pi, 3(4)Delta, 1(4)Phi and 1(6) Pi states were weakly bound, which well depths were within several hundred cm(-1). The spectroscopic parameters were derived. The SOC effect on the spectroscopic properties was evaluated. The spectroscopic results obtained here could be expected to be reliably predicted ones.