Autoionization and photoionization of $\mathrm{O}{(}^{1}D)$

Single-photon ionization of atomic singlet oxygen $\left[\mathrm{O}{(}^{1}D\right)]$ is investigated between 12 and 18 eV. $\mathrm{O}{(}^{1}D)$ is efficiently prepared by laser photolysis of ozone in the Hartley band regime $(\lambda =270\mathrm{}$ 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 ${\mathrm{O}}^{+}$ is measured. Direct photoionization of $\mathrm{O}{(}^{1}D)$ is not observed between the onset of the first ${(}^4{S}^o)$ and the second ${(}^2{D}^o)$ ionization threshold. Intense resonant features occur below the ${}^2{D}^o$ threshold. These are assigned to LS-forbidden autoionization of Rydberg singlet states by the ${}^4{S}^o$ 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.