Knowledge Bank

The absorption spectrum of the PO molecule in the region 2000 {\AA} to 1550 {\AA} 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 $n\ell$ complexes of PO converging to the limiting ion state $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma +$ of $PO+$. New transitions from the ground state $X2\Pi (v=0)$ to the Rydberg series members, $4s\sigma (v=9and10),5s\sigma (v=0and1),6s\sigma (v=0and1),7s\sigma (v=0),4p\sigma (v=0and1),4p\pi (v=oand1),5p\pi (v=0),6p\sigma (v=0),6p\pi (v=0),7p\pi (v=0),3d\sigma (v=0and1),3d\pi (v=0and1),3d\delta (v=0,1and2)$ and $4d\sigma (v=0and1)$ have been analyzed. An upper limit of the ground state dissociation energy has been lowered to $49090cm-1$. Quantum defects are calculated and the first ionization potential of PO is improved to $67532cm-1$.