New features are revealed in the low-energy photoionization spectrum of Ar by critically combining high photon resolution and differential photoelectron spectroscopic techniques. Two LS-forbidden doubly excited resonances are seen in the 3p(-1)(3/2, 1/2) partial cross sections which exhibit mirroring profiles, resulting in complete cancellation in the total photoionization cross section, as was predicted by Liu and Starace [Phys. Rev. A 59, R1731 (1999)]. These results demonstrate that a new class of weakly spin-orbit induced, mirroring resonances should be observable in partial, but not in total, collisional cross sections involving atoms, molecules, and solids in general.

Angle-resolved Auger and valence photoelectron spectra were measured over a 14-eV photon energy range across the Cl 2 2p ionization thresholds. The measurements were carried out using highly efficient time-offlight spectrometers coupled with photons from the Atomic and Molecular undulator beamline of the Advanced Light Source and an advanced data-acquisition system. Auger-electron spectra of 2p→* and 2p→nl resonances were analyzed and the evolution of the resonant Auger to the normal Auger decay distorted by postcollision interaction was examined. We find that valence photoionization channels do not resonate strongly at the photon energies of the core-to-Rydberg excitation, in contrast to the strongly resonating ones observed in the HCl molecule. Auger decay spectra of the 2p Ϫ1 * resonances showed no evidence of atomic transitions in Cl*, also in contrast to HCl. In addition, angular distribution of the photoelectron and Auger-electron lines was derived.