Knowledge Bank

Photoelectron spectra provide transition energies between the molecular ground state and various ion states. Vacuum ultraviolet absorption spectra provide transition energies between the molecular ground state and the different molecular excited states. In the past, the two types of spectra have been used together to construct molecular state energy level $diagram1,2$ However, there has been little done to justify this approach. A justification is presented that requires the evaluation of an ``interaction difference term”. This term is evaluated using atomic energy $levels.3$ Then a simple molecular system is presented and the interaction difference examined.