FIRST AND SECOND ORDER CORRECTIONS TO THE DIPOLE APPROXIMATION 
OBSERVED IN NEON BELOW 1000 EV

O. Hemmers, P. Glans, H. Wang, S.B. Whitfield, D.W. Lindle, 
R. Wehlitz,* I.A. Sellin,* A. Derevianko,# W.R. Johnson#

Department of Chemistry, University of Nevada, Las Vegas, Nevada, USA
*Department of Physics and Astronomy, University of Tennessee, Tennessee, 
USA
# Department of Physics, University of Notre Dame, Notre Dame, Indiana,
USA

Strong deviations in angular distributions of Ne 2s and 2p photoemission
from the dipole approximation have been observed at photon energies below
1000 eV. In the first-order correction two new parameters, arise from
dipole-quadrupole interferences. Second-order corrections are
characterized by four parameters. We found that first and second-order
corrections are necessary to satisfactory describe the Ne n = 2 angular
distributions.