OBSERVATION OF RYDBERG-VALENCE MIXING IN HIGH-RESOLUTION SYMMETRY-RESOLVED OXYGEN K-EDGE SPECTRA OF O2

High-resolution symmetry-resolved O K-edge spectra of O2 have been obtained by collecting fragment ions emitted parallel (DELTALAMBDA = 0) and perpendicular (DELTALAMBDA = +1) to the electric vector of the incident light. In the DELTALAMBDA = 0 spectrum some unassigned peaks are found in the 1s-3psigma Rydberg state, converging to the 4SIGMA- ionized state, on the resonance feature around 541 eV. Comparison with ab initio potential energy curves indicates that the 1s-3psigma(4SIGMA-) Rydberg state is mixed with the 1s-sigma* repulsive state with the same ion core (4SIGMA-) and the avoided curve crossing enhances vibrational excitations. The resonance feature around 539.5 eV is attributed to the 1s-sigma*(2SIGMA-) state arising from the exchange splitting in the 1s-sigma* excitations.