Double-resonance spectroscopy of transitions between autoionizing levels of atomic oxygen

Double-resonance spectroscopy is used to study transitions between autoionizing levels of atomic oxygen. The first laser is used to produce oxygen atoms in the 1s22s22p41D2 level by photodissociation of N2O and to excite two-photon transitions from the 1D2 level to the long-lived (2D degree)3p 1F3 autoionizing level. The second laser is used to probe transitions from the 1F3 level to higher-energy autoionizing levels as well as to the O+D degree direct-ionization continuum. The transitions are detected by using a magnetic bottle electron spectrometer to monitor photoelectrons selectively with the kinetic energy specific to the process of interest. New transitions to the (2D degree 5/2,3/2)ns' and nd' Rydberg-series members with n=16--31 are observed. The intensity dependence of these results has also been studied, and the implications of this relatively low-power measurement for above-threshold ionization are discussed