New valence and Rydberg states of the P18O molecule

The absorption spectrum of the P¹⁸O molecule has been studied in the region 1650–1800 Å. The upper levels of the transitions are shown to be levels of new ²Π valence, ²Π Rydberg and ²Δ Rydberg states of the PO molecule. Most of the levels are perturbed; some of them are predissociated. The new valence state P²Π corresponds to a regular state of the electronic configuration $\text{σ}{}^2\text{π}{}^3\text{π}{}^{12}$ and the ²Π and ²Δ Rydberg states belong to the 5p, 3d, 4d complex series. Perturbations of the P²Π state are shown to arise from Rydberg ～ Non Rydberg interactions with states of same or different symmetry. The complexity of the interactions does not allow to carry out a deperturbation but a comparison with the data of the P¹⁶O molecule allows to give a vibrational assignment to the levels of the P²Π state.