Anomalous multiplet-splitting intensity ratios in K-level x-ray photoemission spectra of NO and O₂

The intensity ratios of the multiplet-split N1s peak of NO and O1s peak of O₂ in the x-ray photoemission spectra of these paramagnetic molecules were found to exceed the simple multiplet ratios (S+1) / S. Hartree-Fock calculations were performed on the ground state and the 1s-hole states in each case, and total overlap probabilities for the passive orbitals were computed. Positive deviations from the multiplet ratios were obtained, but they were smaller than the experimental deviations. The NO(N1s―,³Π / ¹Π) ratios were 3.43 (8) (expt.), 3.09 (calc.), and 3 (multiplet), while for O₂(O1s―,⁴Σ / ²Σ) the ratios were 2.47(3) (expt.), 2.28 (calc.), and 2 (multiplet). Thus incomplete overlap accounts for some, but not all, of the observed deviation. Another consequence of incomplete overlap is multiple excitation during photoemission. The total probabilities for multiple excitation were computed as 0.25(NO,N1s―), 0.28(NO, O1s―), and 0.42(O₂, O1s―), in agreement with the observation by Carlson et al. of large multiple-excitation probabilities.