Experimental verification of quadrupole-dipole interference in spin-resolved photoionization

Khalil T, Schmidtke B, Drescher M, Müller N, Heinzmann U. Experimental verification of quadrupole-dipole interference in spin-resolved photoionization. PHYSICAL REVIEW LETTERS. 2002;89(5): 53001.We have measured the spin polarization of Xe (4p)(-1) photoelectrons after ionization with circularly polarized light at photon energies close to the ionization threshold where a resonant enhancement of quadrupole transitions has recently been predicted. At a reaction angle of 90degrees a nonvanishing longitudinal spin polarization component of about 4% clearly indicates a quadrupole contribution to the photoexcitation. This is the first experimental evidence for the influence of nondipole transitions on the photoionization process at excitation energies much below 1 keV in an observable other than the intensity angular distribution