Electron impact excitation cross sections of sodium autoionizing state from threshold to 1.5 keV

Relative excitation cross sections of the lowest-lying autoionizing state of sodium are measured for electron impact in the range of incident energy from 1.5 keV down to the threshold. Absolute cross sections are obtained by normalization of the relative cross sections at to the theoretical cross section in the plane-wave Born approximation with accurate atomic wavefunctions. Negative ion resonances near the excitation threshold are observed and reproduced by a 26-state R -matrix calculation. The cross sections at intermediate incident energies are obtained in the distorted-wave Born approximation and are compared with the present experimental values and with theoretical values of other authors.