Observation of Rydberg-Valence Mixing in High-Resolution Symmetry-Resolved Oxygen $K$ -Edge Spectra of $O_{2}$

High-resolution symmetry-resolved O

K

-edge spectra of

O_{2}

have been obtained by collecting fragment ions emitted parallel (

Δ Λ = 0

) and perpendicular (

Δ Λ = + 1

) to the electric vector of the incident light. In the

1 s - 3 p σ

spectrum some unassigned peaks are found in the

1 s - 3 p σ

Rydberg state, converging to the

{}^{4}Σ^{-}

ionized state, on the resonance feature around 541 eV. Comparison with ab initio potential energy curves indicates that the

1 s - 3 p σ ({}^{4}Σ^{-})

Rydberg state is mixed with the

1 s - σ^{*}

repulsive state with the same ion core (

{}^{4}Σ^{-}

) and the avoided curve crossing enhances vibrational excitations. The resonance feature around 539.5 eV is attributed to the

1 s - σ^{*} ({}^{2}Σ^{-})

state arising from the exchange splitting in the

1 s - σ^{*}

excitations.

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Observation of Rydberg-Valence Mixing in High-Resolution Symmetry-Resolved OxygenK-Edge Spectra ofO2