Knowledge Bank

Ab initio spin-orbit configuration interaction calculations are performed on the $UO2$ molecule, which has been observed in matrix isolation and laser ablation vacuum ultraviolet spectroscopic studies. We found the ground state to be $5f17s1\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Phi 2u$. There are four excited states below $32,000cm-1$ that have large transition moments with the gound state. The highest of these excited state is $5f1\sigma u1\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Phi 2g$. It has two minima in its potential curve. The $\sigma u$ orbital at the minimum with shorter bond distance has mostly 7p character, while it has mostly 5f character at the longer bond distance minimum. There are only a few dipole-allowed emission lines from this state to lower-energy states. Most electronic states in this region of the spectrum have g symmetry because most of the orbitals involved (5f,7s,7p) have the same (u) inversion symmetry.