The O 1s photoelectron spectrum of molecular oxygen revisited

High-resolution photoelectron spectra of the inner-shell levels of molecular oxygen have been measured using synchrotron radiation. The vibrational structure of the two magnetically-split core-shell components is analyzed based upon ab initio calculations. The ratio between the intensities of the two components was analyzed at several different ionization energies up to about 600 eV, and the same is discussed and compared to high-energy ionization intensities. A theoretical calculation shows very good agreement with the measured spectra. The calculation implements a model where two parity components make up the ⁴Σ peak profile. The gerade-ungerade energy split for this state is found to be 50 meV.