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