The possibility to symmetry assign x-ray absorption spectra using x-ray emission spectroscopy is demonstrated. The oxygen $K$ spectra of ${\mathrm{CO}}_2$ are used to illustrate the possibility to assign core excitations through excitation-energy and angular dependence of resonantly excited x-ray emission spectra. The Rydberg-associated structures just below the ionization threshold in the O $K$ x-ray absorption spectrum are assigned to be mainly due to excitations to orbitals of ${\sigma }_g$ character. The results, which contradict some previous literature assignments, are supported by quantum-chemical calculations.

• Received 12 August 1996

DOI:https://doi.org/10.1103/PhysRevA.57.864