Combining the linearly polarized high-flux photon beam of a dye laser and the synchrotron radiation of a vacuum-ultraviolet undulator, lithium atoms have been aligned and excited to Li 1snln’l’ core resonances. The angular distribution of the electrons emitted upon the decay of these resonances strongly depends on their symmetry character. Exploiting this dependence, the symmetry of Li 1snln’l’ core resonances has been determined. The results allow for stringent tests of theoretical predictions and demonstrate the great potential of angular-resolved photoelectron spectroscopy on aligned atoms.

• Received 9 September 1991

DOI:https://doi.org/10.1103/PhysRevLett.68.2285