Autoionization and photoionization of O(¹D)

Single-photon ionization of atomic singlet oxygen [O(¹D)] is investigated between 12 and 18 eV. O(¹D) is efficiently prepared by laser photolysis of ozone in the Hartley band regime (λ=270 nm). It is subsequently ionized by using monochromatic radiation, which is generated in a laser-produced plasma. Time-of-flight mass spectra are recorded and the photoion yield of O⁺ is measured. Direct photoionization of O(¹D) is not observed between the onset of the first (⁴S^o) and the second (²D^o) ionization threshold. Intense resonant features occur below the ²D^o threshold. These are assigned to LS-forbidden autoionization of Rydberg singlet states by the ⁴S^o continuum. The relative intensities of autoionization resonances are compared to the corresponding optical oscillator strengths. The results are discussed in terms of the autoionization efficiency of Rydberg states.