Rydberg states of the PO molecule

The absorption spectrum of the PO molecule in the region 2100 to 1550 Å has been studied in detail at high resolution. From a rotational analysis of the spectrum, a number of new electronic states have been discovered. Some of these electronic states have been assigned to Rydberg series of the various nl complexes of PO. An upper limit of the ground state dissociation energy has been lowered to 49090 cm^?1 (X²Π, T₀ = 0). Quantum defects are calculated and the first ionization potential of PO is improved to 67 532 cm^?1.