Anomalous multiplet-splitting intensity ratios inK-level x-ray photoemission spectra of NO andO2

Abstract

The intensity ratios of the multiplet-split $\mathrm{N}1s$ peak of NO and $\mathrm{O}1s$ peak of ${\mathrm{O}}_2$ in the x-ray photoemission spectra of these paramagnetic molecules were found to exceed the simple multiplet ratios $\frac{\mathrm{}(S+1\mathrm{})\mathrm{}}{S}$. 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 $\mathrm{NO}(\mathrm{N}\overline{1s},\frac{{}_{}{}^3{}_{}{}^{}\Pi }{{}_{}{}^1{}_{}{}^{}\Pi })$ ratios were 3.43 (8) (expt.), 3.09 (calc.), and 3 (multiplet), while for ${\mathrm{O}}_2(\mathrm{O}\overline{1s},\frac{{}_{}{}^4{}_{}{}^{}\Sigma }{{}_{}{}^2{}_{}{}^{}\Sigma })$ 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 $0.25(\mathrm{NO},\mathrm{N}\overline{1s})$, $0.28(\mathrm{NO},\mathrm{O}\overline{1s})$, and $0.42({\mathrm{O}}_2,\mathrm{O}\overline{1s})$, in agreement with the observation by Carlson et al. of large multiple-excitation probabilities.