STRUCTURED EFFECTS OF RYDBERG-RYDBERG ROTATIONAL COUPLING ON INTENSITIES IN THE ZERO ELECTRON KINETIC-ENERGY THRESHOLD PHOTOIONIZATION SPECTRUM OF STATE-SELECTED NO2

Transitions from individual rovibrational levels of the 3p-sigma 2-SIGMA(u)+ state, selected by double resonance, yield rotationally resolved threshold photoionization spectra of NO2. Observed photoionization cross sections conform with simple angular-momentum selection rules for transitions from aa well-defined Hund's case b intermediate state to the case d Rydberg states that lie just below each successive threshold, except for the appearance of anomalous lines corresponding to large negative changes in ion-core rotational angular momentum. These latter transitions are found to be structured, and this structure is shown to reflect a Rydberg-Rydberg coupling hierarchy induced in zero field by the quadrupole moment of the finite core and facilitated in its final discrete-discrete step by low-field Stark mixing.